STEP 2- Download Kies here http://www.samsungapps.com/about/onP...UNTRY_CODE=GBR This will install the usb drivers needed for the flashing so install after downloaded.
STEP 3- Download Latest samsung UK Simfree firmware here http://www.multiupload.co.uk/LSLRGURR57 There is no Password Just put extract the .tar file in the zip archive and put it as the PDA in odin and reboot your phone to download mode
STEP 4- Connect the USB cable and Turn your device on with volume down, action and power pressed - press 'up' at the warning prompt Run the Odin EXE you just extracted from the ZIP.
STEP 5- Only 1 file must be loaded in the PDA box the file as follows For PDA load, I9100XWKDD_I9100XXKDH_I9100XEUKD1_HOME.TAR
NOTE(PLEASE TAKE A LOOK AT THE PIC BELOW AND AND MAKE SURE THAT YOU REPLICATE THE SAME SETTINGS AS IN THE PIC AND YOUR GOOD TO GO)
STEP 6- You should have a yellow box on the left side in Odin if you have followed this guide this means you are ready to flash. Please make sure your battery is full wait for any drivers to load and the yellow box on the left should be there if it isnt you have not installed Kies STEP 2 if you have the yellow box on left proceed by pressing start on Odin and relax.
STEP 7- Odin will display a progress meter on Odin and on the phone be patient while it flashes all the required files once done it will reboot the phone and goodbye o2 logo on boot and shutdown. When the phone finally boots back complete setup. And there you have it a fully debranded samsung galaxy s2 hope it was easy to follow enjoy.
STEP 8- One last final step is to change your CSC code by typing this code in the phone dialer *#272*<your IMEI># (the code will be listed at the top of the screen. If you're coming from O2 PAYG handset it should say O2U. Now Enter recovery (volume up, home, power keys together) and do a factory reset and choose reboot phone Check your CSC code again Hopefully it will now say XEU
Rebrand your firmware back to O2 original firmware for warranty purpose or you just want to go back to o2 original rom download it here http://www.multiupload.com/VHX20NJEAP There is no password extract the zip file to the desktop you should end up with I9100XWKDD_I9100XXKDH_I9100O2UKD1_HOME.TAR The procedure is the same as above just start from STEP 4 above skip STEP 8 use the same settings as shown in the pic below enjoy.
latest official UK firmware
CSC:XEUKD1 (XEU csc)