Tap Reboot System . The first boot to Android 5.1.1 will take . Do not touch the phone. You will see the CyanogenMod or custom boot animation.
Official updates for the I9100 stopped at Android 4.1.2 Jelly Bean. To get Android 5.1.1, you must use Custom ROMs developed by the community. Matthias Kerstner Stable Options CyanogenMod 12.1 (CM 12.1) : The most popular choice for Android 5.1.1 on this device. gti9100 firmware 511 download upd
Navigate using the volume keys and select the Power button to execute a Wipe Data / Factory Reset . Tap Reboot System