1. At the beginning, turn off the phone by holding the Power button.
2. Then press and hold Volume Up + Home button + Power button until you see logo of your phone.
3. Release held buttons the Recovery Mode menu appears.
4. Afterwards from the menu choose "Wipe Data/Factory Reset" by using Volume buttons to scroll and Power button to select options.
5. Confirm the whole operation by tappinng "yes".
6. Select "reboot system now" to restart the phone
7. Success! The hard reset has just been performed

Second method:

1. If the display is off, press the Power to turn it back on. 
2. Find and select Settings and then go to User and Backup.
3. Tap Factory Data Reset
4. Confirm all information on your screen.
5. Well done!