Restoring the default settings or factory reset your device will delete all your existing files. It is recommended to backup your important files on your computer before attempting to reset your device.
>>> Switch on your device.
>>> Go to Menu > Settings > General tab
>>> Select Backup & Reset > Restore Factory Settings > Reset phone.
>>> Your device will reset to factory settings, and reboots.
>>> Turn off your phone.
>>> Press and hold together Volume Down + Power button, or Volume Up + Power button.
>>> Once Recovery menu appears on the screen, release the buttons.
>>> Select "wipe data/factory reset" by using Volume buttons, and Power button to confirm.
>>> Then choose "Yes -- delete all user data".
>>> Confirm operation "reboot system now".