CyanogenMod 12 for Samsung Galaxy S3 GT-I9305 is brought to you by xda Recognized Developer DerTeufel1980.
CyanogenMod 12 is a custom ROM based on Android Lollipop 5.0.2.
Installing custom ROM requires a custom recovery to be installed on your device, which may VOID your warranty and may delete all your data. Before proceeding further you may consider backup your all data. You are the only person doing changes to your phone and I cannot be held responsible for the mistakes done by you. Neither the developer nor we will be held responsible for any disaster that happens to your device.
Files needed to install cyanogenmod 12 for galaxy s3:
Installation guide of CyanogenMod 12 for Galaxy S3:
Copy the CyanogenMod ROM and GApps zip file to your SD card or internal memory (By using a USB cable or via adb push command).
Reboot your phone into recovery mode (Hole Volume UP + HOME + Power button while the phone is booting)
Or if you have a PC in hand with USB driver installed for your phone then type the following command to enter into recovery mode:
$ adb reboot recovery
Wipe data/factory reset.
This will delete all your data on your phone.
You may consider backing up your phone data or take a nandroid backup.
Select the Install Zip from sdcard option.
Select the CyanogenMod ROM zip and then followed by the GApps zip file.
The flashing may take a while.
When it will be done you can reboot your system and enjoy the Cyanogenmod 12 (Android Lollipop) for Galaxy S3 GT-I9305.