* Here's why you need CU at least. And ideally FCU, giving you yet another six months of support and patches, right to the end of 2019.
In what follows, I explicitly refer to the Lumia 830, but in principle this will also work with the Lumia 735.
It may be that you've been playing with one of these smartphones after going through the Insiders programme and then used the Windows Device Recovery Tool (WDRT), after which your phone is taken right back to the last officially supported software, in this case Windows Phone 8.1 (hey, the phones themselves are from 2014!), so before you even start the body of this article you may have an extra step to do, getting the phone onto a branch of Windows 10 Mobile.
If you're already on Windows 10 Mobile, perhaps AU, which is how far Microsoft lets you go officially, then you can skip to step no. ??? below.
If you're back on Windows Phone 8.1, just for completeness:
1. A year ago, the on-device Upgrade Advisor still worked, but Microsoft seems to have switched off whatever this hooked directly into, somewhere in Seattle. So use the Over-The-Cable Updater tool instead on any convenient Windows PC. Don't worry, this is all 100% official still. This requires no initial interaction other than plugging in the Lumia 830 (which won't show any unusual connection, all the action happens in the Command window on the PC).
After the OTCUpdater has worked its magic, your 830 then has all the OS update files in its internal storage.
2. In Settings on the phone, head for the usual 'phone update' and you should see the upgrade process already underway. Wait. And then wait some more. Follow any prompts. Wait some more. Tip: do this with a good book or a TV programme handy!
Once on Windows 10 Mobile, you'll be on an early branch of the OS, dubbed '1511' (2015, November, builds 10586.nn), so don't worry too much about setting everything up and customising it, as you have a long way to go before you're done today!
3. In Settings, head for 'Updates & Security' and check for updates again - you'll see another update, this time taking you from '1511' up to a baseline build of AU (builds 14393.nn).
4. Again in Settings, check again and you'll see another small patch after this (build 14393.2551, at the time of writing), putting on the latest tweaks and security patches (though, in theory, no more patches to AU are expected for 2019). Although you don't strictly need this, best to apply it anyway, just in case the OS tries installing it while you're doing other stuff below!
Your Lumia 830 is now on the latest build Anniversary Update and Microsoft would say 'Stop there, you're done!' you're ready to start the geeky fun...
5. Warning. Before going further, pay attention because here's a geek-factor warning.
- If you don't know what a 'Command Window' is or don't own a Windows PC then please don't do any of this!
On the other hand, if you know what a Command Window is, own a Windows PC, and are happy looking into files and folders using Windows Explorer (or similar), then you're geeky enough and have everything you need to do the sequence below. It doesn't take long if everything goes smoothly, but I'm assuming that as you do have the geek factor then you'll not panic if something doesn't work first time and you'll work through it logically without emailing me!
6. Before doing any of this, it's worth doing a full backup in Settings/Update & Backup/Backup/Backup options - just in case. You shouldn't lose any data, but there will be the temptation once you're on CU or FCU to do a full 'reset your phone', for optimum performance, and then you'll appreciate that there's a full backup of your apps and preferences ready and waiting.
NB. I've adapted and expanded on instructions from several sources, but principally here. Note that when running Interop Tools, you'll always get a pop-up at the start - each time, just choose 'This device', on its own, i.e. not 'This device (with provider extensions)':
7. On your Windows PC, grab a recent version of Interop Tools from here, it'll unzip to a main app and five dependencies, all in a sub-folder.
8. On your Lumia 830, enable Developer mode in Settings/Updates & Security/For Developers. Then enable Device Portal. And then toggle off 'Authentication':
9. Access the IP quoted on your PC/laptop’s browser of choice. The IP address looks like http://192.168.0.x In your PC's browser you should now see the phone's built-in portal (bet you didn't know that was there, eh?!)
10. In the portal interface, click on 'Apps' and then scroll down to the 'Install app' section. If your PC browser interface becomes unresponsive then this may be because your phone has locked. So keep the latter alive and the display on.
11. Using the file-picking fields, select the Interop Tools app file (from step 1, above, the one you want is about 40MB and is the one without 'th1' in its filename), then scroll down a little further and add each of the five dependency files in the appropriate file picker (in each case 'Add dependency' and then click on 'Browse', etc., picking the APPX files from the 'arm' sub-folder. You should have six files selected and their paths shown.
12. Again, double check that your Lumia screen is still active - make sure it stays alive throughout. Click on 'Deploy/Go' and wait a minute (sometimes there's a literal wait for a minute while the uploads get going) while Interop Tools and all the bits it needs are installed on your phone. Once finished 'installing' (again, be patient!), you should see 'Interop Tools (Preview)' in your phone's app list.
13. Back on the phone, open Interop Tools and accept the various permissions asked for. Again, when you get to 'Select a provider for this application session', pick 'This device' from the four options given, and then tap on 'Use this provider'. Wait a few seconds for the utility to initialise, there's a lot going on behind the scenes - don't ever rush Interop Tools!
14. On the hamburger menu, under 'Unlock', go into the 'Interop unlock' pane.
15. Enable 'Restore NDTKSvc'. The toggle will be set.
16. Restart the phone. Power it down, then power it up. In Interop Tools, check the Interop Unlock section again, you should see 'Restore NDTKSvc' still enabled.
17. From the hamburger menu, go to 'Registry'/'Registry Browser' and then go into 'HKEY_LOCAL_MACHINE/System/Platform/DeviceTargetingInfo'
18. Change three of the registry keys as follows:
- 'PhoneManufacturer' - change the 'Registry Value Data' from 'NOKIA' to 'MicrosoftMDG' (capitalisation is important). Tap on 'Write' (the tick control).
- 'PhoneManufacturerModelName', change this from 'RM-984_1047' (or similar - if yours is different, then make a note of it exactly, on a piece of paper!) to 'RM-1085_11302' (mimicking a Lumia 950 XL, or RM-1116_11258 has been suggested for dual SIM devices, again mimicking a Lumia 950 XL variant). Again, tap on 'Write'.
- 'PhoneModelName', change this from 'Lumia 830' to 'Lumia 950 XL'. Tap on 'Write'.
19. Go to the phone's 'Settings'/'Update'/'Check for updates', as usual, and you should see 15063.xxx, the Creators Update (branch '1703', as in '2017 March'), installing already.
20. After installation, check for updates again, to get, in sequence, the Fall Creators Update (branch '1709') baseline, and then the latest build/patch. This will all take an hour or so, so have something else productive to do while you wait!
Note that this is all genuinely uncharted territory for the Lumia 830 (or 735) - don't expect fully optimised performance on these newer branches of Windows 10 Mobile when your phone only has 1GB RAM - heck, Windows isn't always smooth on the Lumia 950 range with 3GB RAM!
21. Once fully installed and up to date, revert the registry settings, in Interop Tools, to their original values, using the Registry Browser and the keys mentioned above. In this case (respectively), "NOKIA", "RM-984_1047" (or similar), and "Lumia 830".
That way, any software you install that goes looking won't suddenly think your phone has Lumia 950 XL hardware! Don't worry, now that your Lumia 830 is on Fall Creators Update you'll get all the monthly security patches and fixes until Autumn 2019 or beyond. Which is pretty decent for a phone that shipped in the 2014 timeframe, i.e. four years ago!
22. For completeness (and peace of mind), in 'Settings'/'Updates & Security'/'For Developers', check 'Device portal' is off again and also then set the phone's status back to just 'Windows Store apps'.
Now, all may be well at this point. All your data, the latest updates, and so on. In which case you're done.
However, if you do suspect that there are problems under the hood - after all, you have just jumped through a year or more's worth of OS updates in a couple of hours and the FCU may be battling with system files created under AU (and, for this full tutorial, under Windows Phone 8.1) - then I'd suggest a full 'reset your phone' in Settings/System/About, followed by signing back into your account and choosing the backup that you made earlier. Yes, it'll take ages (over 100 apps to install in the background and foreground), but it'll be worth it.
Or you could do what I often do and that's build the phone up again, installing applications as you need them, i.e. not reinstalling all the junk apps that you'd grabbed in the past 'just to try out'. A fresh start under FCU. It's up to you, anyway!
Comments welcome, especially if you think I missed a step or a subtlety that might improve this article. Please don't email me with requests for individual hand-holding though - you're in ultra-geek territory here and you need to work through all this yourself.