1) Install USB Drivers for Galaxy S2 to transfer files between the Android device and the computer.
2) Enable USB Debugging Mode on the phone to connect it with the computer and use Android SDK with it. [Press Menu>> Settings>> Applications. From there, navigate and click on Development option and then check the USB Debugging Mode.]
3) As the tutorial might wipe out all data of the phone, create backup. If the device is having any custom recovery such as ClockworkMod or, TWRP then backup data using the same.
4) If the Android phone powers off due to lack of battery during the process, it could damage the device. Therefore, the Galaxy S2 should have charge above 80% battery charge.
6) Android 4.4.2 KitKat Carbon nightly build works only with Samsung Galaxy S2 GT-I9100. As applying this to any incorrect variant might brick the device, verify the model number of Galaxy S2 by navigating to Settings>> About phone>> Model number.
7) After flashing the ROM, if the device gets stuck on Booting animation or experience boot loop then perform wipe cache partition and wipe dalvik cache for a few times before rebooting the device.
8) Once the ROM is installed, users are advised to give 10 minutes to the ROM after the device boots up for the first time for a better user experience.
How to install Android 4.4.2 KitKat on Galaxy S2 GT-I9100 with Carbon nightly
Step-1: Connect Galaxy S2 to the computer using USB cable then copy both downloaded zip files to the internal storage of the phone. But do not extract/unzip the files
Step-2: Unplug the USB cable from the phone and switch it off
Step-3: Boot the phone into CWM or, TWRP recovery mode by pressing and holding Volume Up,Home and Power buttons together
Step-4: Create a Nandroid backup of the current ROM which can be restored later if the new ROM does not work or users wish to go back to the previous ROM.
CWM-Select backup and restore then name the file and confirm the process
TWRP- Press backup, set a name and swipe to confirm the backup
Step-5: Perform a Factory Reset. This will wipe all data from system partition, which means the device will lose all installed apps data and the other system files. [Factory Reset does not delete contents from internal or external storage.]
CWM- Select wipe data/factory reset and confirm the process
TWRP-Press Wipe then confirm the process
Note: Do not skip this process as the new ROM might not boot into normal mode.
Step-6: Install the carbon KitKat nightly ROM on Galaxy S2.
CWM- Select install zip from sdcard then choose zip from sdcard. Now browse to the location where Android 4.4.2 ROM file is saved. Select it and confirm installation
TWRP- Press Install, browse to the location where the Carbon ROM is saved. Then Swipe to confirm the process
Step-7: When the ROM is installed, follow the similar process and flash Gapps file
Step-8: After the installation process is completed, return to the custom recovery screen and reboot the phone into normal mode. Note that the first boot will take a few minutes, therefore, you should not press any button until the home screen of the new ROM appears
Carbon nightly featuring Android 4.4.2 KitKat should now be installed on the Galaxy S2. Navigate toSettings>> About phone to verify the new software version of the device.
If the first boot process takes longer time than usual to cmplete, repeat the entire procedure again. Apply Factory Reset then apply Format/System option also.
If you do not like the new ROM, you may always choose to restore your phone to the previous firmware version using the back-up files created in step-4. Use the custom recovery mode to restore the previous ROM.