With phone turned OFF, press the Home key and Power button simultaneously. The device will power on. Keep holding the buttons downuntil Recovery screen (exclamation mark in triangle with android figure) appears.
Press the Search key.
Touch wipe data/factory reset then touch Ok.If the touch screen is not functioning, utilize the Volume key (up/down) to highlight and the Camera key to select.
Touch Yes--delete all user data and touch OK.This will bring back the device to factory settings.
Turn off your phone.
Now press and hold this buttons: Volume Up + Volume Down + Power button.
When Android green man apper in your screen, then press Home button.
Next select option "wipe data/factory reset" using Volume keys to hightlight option, and Power button to confirm.
Then choose and confirm option "Yes -- delete all user data".
After that to finish operation confirm option "reboot system now".