Turn off your phone. Now press and hold this buttons: Volume Up + Volume Down + Power button. When you see menu with 2 options, then release holded buttons. Then choose option "Recovery mode" by pressing Volume Up key. Next select option "wipe data / factory reset" using Volume Down to navigate, and Menu key to accept option. Accept this "Yes -- delete all user data", and wait. Afterwards confirm operation "reboot system now". The end! WARNING ! Hard Reset will erase all of your data , All described operations you are doing at your own risk.