Before you try the factory reset or hard reset on your device, make sure that you have backup your important files. Restoring the default settings or factory reset your device will delete all your existing files and will go back to its initial state.
Factory Reset:
>>> 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.
Hard Reset:
>>> 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.