Users of Samsung’s older Galaxy S3 device can now enjoy Android 6.0 Marshmallow with a custom AOSP made available. Because of the smartphone’s hardware configuration, it is incapable of receiving an official update or any further Android support.
AOSP custom ROM is developed by Haynox team from the AOSP port. Before you can begin the installation process for this beta AOSP version, confirm that your Galaxy variant is I9300.
2. Plug in your Galaxy device, then to the phone’s storage copy the downloaded files.
3. Unplug the S3 from the PC. Then using the Quick Boot app available on the Playstore, boot the device into recovery mode. Alternatively, simply press down the Power, Home and Volume Up buttons simultaneously.
4. Once on Recovery mode, create a full backup of all the data on your device. On the recovery mode menu choose Backup then to confirm, swipe the bottom of the screen.
5. When the backup process is over, delete all Galaxy S3’s data. To do this, select Wipe then the Advanced wipe option thereafter choose Dalvik Cache, System, Data then once in the Cache option, swipe to start the data deletion process.
6. Go to the recovery menu and select install; go to the CM13 ROM stored on your device and confirm installation by tapping the flash option.
7. Once the ROM installation is complete, repeat the same process to install GApps.
After the complete installation, tap Reboot system to restart the Galaxy S3. Now your Samsung Galaxy S3 is upgraded to Marshmallow.