For those of you who want to unroot to official ICS on your AT&T Galaxy S2 SGH-i777, here’s how to do that using ODIN. This will get everything back to stock including your recovery but you can always re-root it easily.
If you don’t want to lose ClockworkMod Recovery and Root, you can also flash the CWM-zippable official ICS update in ClockworkMod Recovery.
Step 1. Plug in a micro-USB cable from your computer to your AT&T Galaxy S2 SGH-i777. Then hold down Volume Up, Volume Down, and Power buttons together for about 10 seconds.
Step 2. When you see the warning sign hit Volume Up button to enter ODIN Download mode.
Step 3. Download ODIN and AT&T official tar file:
Unzip the ODIN zip file and also the ICS tar file. Run the ODIN program.