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.
>>> Go to Settings app, and tap General Settings
>>> Select Backup & reset, then tap Factory data reset
>>> Choose Reset phone.
>>> Accept all information on your screen.
>>> Turn off your phone.
>>> Then press and hold together Volume Down + Power button.
>>> Release the buttons once you see the reset menu.
>>> Select option Recovery mode using Volume Down to browse, and Volume Up to accept.
>>> When you see Android logo with the red hazard box, press the Power button to enter to Recovery mode.
>>> Then scroll to option "wipe data/factory reset" using Volume Down to navigate, and Volume Up to confirm.
>>> Select option "Yes -- delete all user data".
>>> Choose "reboot system now" using Volume Up to confirm.