AOKP ROMs or Android Open Kang Project are one of the favourites used to update devices or change from stock to custom ROMs. AOKP ROMs are basically fast, very steady, and based on the AOSP release of the Android OS.
Below are the how-to instructions on updating a Samsung Galaxy S2 to Android 4.2.2 Jelly Bean, using an AOKP build custom ROM.
Prerequisites and reminder:
1. This how-to instructions is exclusive for Samsung Galaxy S2 I9100. Do not try this with other variants of Galaxy S2.
2. Connect your Galaxy S2 to the computer using a USB cable.
3. Copy the downloaded Android 4.2.2 zip file and the Google Apps zip to the SD card. Place the files in the SD card root folder, not to another folder.
4. Switch off the device and disconnect it from the USB cable.
5. Switch on the phone while pressing and holding these keys: Volume UP + Menu + Power buttons. Wait till the device boot to the Recovery mode.
6. In the ClockworkMod recovery mode, perform a full data wipe first.
7. Scroll down to "flash zip from SD card". Use the Power button to select the zip file.
8. Use the Volume keys to navigate around and find the Android 4.2.2 zip file in the SD card. Use the Power key to select the zip file.
9. Confirm the installation on the next screen, and wait till the process is finished. Repeat the same process of selection and installation with the Google Apps zip file.
10. After the installation is completed, "Go back" and reboot the device. Select "Reboot system now" from the recovery menu. The device will boot within 5 minutes for the first time of use. Be patient.
11. After that, check the device information if its successful. Go to Settings > About Phone to view the details.
Separate AOKP versions for other Galaxy S2 variants are also available here. Make sure that you have every requirement noted because there are certain things needed before flashing an update for those variants.