From the Lumia Conversations post:
Starting today, the Lumia Denim update is rolling out to Lumia Icon devices in the United States over the Verizon network.
If you’re one of the many Lumia Icon owners in the U.S.—and that includes yours truly—it’s reason to rejoice. You’ll skip Lumia Cyan altogether and go directly from Lumia Black to Lumia Denim in the Windows Phone operating system.
You’ll get the latest Windows Phone 8.1 goodies including Lumia Camera, which gives you 4K video recording capability and a super-fast shutter speed, among other camera features; Live Folders; and plenty of other improvements.
Updating your Lumia Icon
Before you download Lumia Denim, you need to free up at least 1GB of storage space on your Lumia Icon. To do so, move some apps and games to a memory card and large files such as videos to OneDrive.
Next, check whether Lumia Denim is available for your Lumia Icon by going to settings on your phone and scrolling down to phone update. Tap check for updates. While you’re on that screen, it’s also helpful to tap the square that automatically downloads updates to your phone.
One has to chortle a tiny bit at Microsoft's expense, since the Icon doesn't HAVE a 'memory card' to move files to! A little too much copying and pasting from the Conversations team, one has to think....
In fact, for a major OS upgrade, especially one that skips a generation, I'd recommend that any affected users clear at least 3GB - just in case. The new ROM itself is well over a Gigabyte and there's quite a bit of messing around to do in the internal storage to effect the update.
Good to see the Icon not forgotten though - Rafe has one, so I'll get him to update his and see how the procedure goes!