Hi, I am Kayyum Patel.
Today I am going to show you that how can you upgrade your old & beloved Samsung Galaxy S3 i9300 to latest Android Lollipop 5.1.1 version using this unofficial Cyanogenmod ROM.
Of course, this will be an unofficial update operation and you will lose the Samsung Galaxy S3 warranty by completing the same. Also, root access must be ensured on your phone, while a custom recovery image must be installed. Else, you won’t be able to apply the guidelines from below for updating your smartphone.
Afterwards you need to make sure that a computer is near you as you will have to use it – of course you need to use your SGS3 and your phone’s USB cable too. On your handset enable USB debugging option by going to “menu – settings – developer options” and avoid any unpleasant situations by temporarily deactivating security protection from your computer. Moreover, charge your phone before going any further. If your device gets turned off in the middle of the update process, it might also get bricked.
The ROM Cyanogenmod 12.1 developed based on Android 5.1.1 is unofficial yet pretty stable though.