1) The device must be switched off, so hold the Power button for a short while.
2) In the next step press and hold together: Volume Up + Home +Power key for a couple of seconds.
3) You should release held keys when the Samsung Logo appears on the screen.
4) After that, select from Recovery Mode menu “wipe data / factory reset” using Volume buttons to navigate and Power button to confirm action.
5)After wipe complete reboot mobile.