Ensure the device is powered off. If the device doesn't respond to input, remove then re-insert the battery.Press and hold the Volume Up button(located on the left edge near the top) and the Home button (located at the bottom in the middle).While continuing to hold the Home andVolume Up buttons, press and hold thePower button (located on the right edge) until 'RECOVERY BOOTING' appears in the upper left then release all buttons. Select wipe cache partition. the Volume Up/Down buttons to highlight and the Power button to select. Select reboot system now. Option is highlighted, utilize the Power button to select. Hope this helps.. This is the process on the current lollipop update..