Remember I'm just sharing what I found here, I still haven't tested it myself but a lot of people have and they say it's working fine. Many thanks to SilverDroid from AndroidForums.com for making this happen and doing the original tutorial.
- Download 2.3.4 Stock Rom from Sam firmware here : Android 2.3.4 for Galaxy S II. - www.SamFirmware.com (password when extracting is samfirmware.com)
- Download ODIN if you don't already have it as you will need this. You can get it from here
- Reboot your phone into download mode. To do this first shut down the device. Then, press and hold the down volume key + home button + power button.
A warning will pop up asking you to confirm if you want to go into download mode (by pressing up) or if you want to cancel (by pressing down) Press up and enter download mode
- Start up ODIN on your pc. From the 2.3.4 RAR file you have download, there will be 3 RAR files inside when you extract. Click on PDA, Phone, and CSC, and choose the 3 files so it loads as below.
PDA - CODE_I9100XXKG1_CL349526_REV02_user_low_ship.tar
Phone - MODEM_I9100XXKG1_REV_02_CL1034110.tar
CSC - GT-I9100-CSC-MULTI-OXAKG1.tar
- Here is a picture so you get the idea though the names are different
- The ONLY boxes that should be ticked are Auto reboot and F. Reset time
- Connect the phone to the PC via a USB cable and wait for the ID:COM box to turn yellow
- Click start to flash the new firmware (Do not disconnect the cable or turn off the device, it will reboot when it has finished)