Hard Reset SAMSUNG I777 Galaxy S II

First method:

1. Make sure, that your phone is on.
2. Then from the home screen, press the Menu key, and then tap Settings.
   
3. Next scroll to and tap Privacy.
4. Now tap Factory data reset.
5. Tap Reset phone.
   * NOTE: Tap to check Format USB Storage to remove all saved media and applications from an inserted Micro SD memory card.
   * If security is enabled, enter your unlock PIN, password, or pattern.
6. After that tap Erase Everything.

Second method:

1. Turn off your cell phone.
   
   * NOTE: If unable to power off, remove and reinsert the battery.
2. Then press and hold 3 buttons: Volume Up + Volume Down + Power button.
   
3. Next release only Power key when you see Samsung logo.
4. Select option "Wipe data/factory reset" using buttons: Volume Up and Volume Down, and to confirm use Power button.
   
5. Now choose "Yes! delete all user data", and confirm with Power button.
   
6. After this operation, select "Reboot system now" and press Power key to confirm to reboot your handset.
   

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.