For those of you who want to unroot your Galaxy S2 i9100 to the latest ICS “official” stock ROM, you can do this easily using ODIN. (or Heimdall for Mac/Linux).
Step 1. Put your Galaxy S2 i9100 into download mode by holding down Volume Down, Center button, and Power button together for about 10 seconds until your phone reboots and you see the warning sign. Press Volume Up button to enter download mode.
Step 2. Connect a micro-USB cable to your Galaxy S2 from your computer.
Step 3. Download stock ICS ROM and unzip(Don’t have unzipping program? Download and install 7Zip.).
Download stock ICS ROM
Step 4. Download ODIN, unzip(Don’t have unzipping program? Download and install 7Zip.), and run the program.
Step 5. When ODIN runs, you should see a yellow highlight with a COM appearing. If you don’t see it, download Samsung Kies and install. Then plug-out and plug in your micro-USB cable to your phone, you should see it now.
Step 6. Choose “PDA” in ODIN and choose the stock ROM file you downloaded/unzipped earlier.
Step 7. Hit “Start” and your phone should start unrooting/unbricking back to ICS official stock ROM.
Step 8. Your Galaxy S2 i9100 will reboot after 5-10 minutes.
Step 9. Your phone should now be on stock ICS.
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You will need a rooted Galaxy S2 to install all ROM/kernels.
NOTE: PLEASE ONLY INSTALL ROMS INTENDED FOR YOUR VERSION OF Galaxy S2! Otherwise you WILL BRICK YOUR PHONE and I will not be responsible!
First time to rooting and custom ROMs?
Please see our FAQ for your Galaxy S2 model FIRST!!!:
Galaxy S2 GT-i9100 FAQ
Galaxy S2 SGH-i777 (AT&T) FAQ
Galaxy S2 SGH-T989 (T-mobile) FAQ
Galaxy S2 SPH-D710 (Sprint) FAQ
Galaxy S2 ROMs
Galaxy S2 GT-i9100 ROMs
Galaxy S2 SGH-i777 AT&T ROMs
Galaxy S2 SGH-T9989 T-Mobile ROMs
Galaxy S2 SPH-D710 Sprint ROMs