Switch your phone off by pushing and holding the power button. If your phone has frozen, remove and replace the battery to reset it (you don't need to remove your SIM card).
Hold down the ‘Power’, ‘Volume Up’ and ‘Menu’ buttons at the same time for approximately 10 seconds. You can release the buttons when the Android logo appears on the screen. This will allow you to access the unlock/reset menu.
To navigate through this menu, use the volume up/down buttons to scroll up and down and the power button to confirm selections.
Scroll down and select Wipe Data/Factory Reset’.
When prompted, scroll down and select ‘Yes - Delete All User Data’.
Your phone will reset to factory settings.
Scroll down to and select ‘Reboot System Now’. Your phone will restart, with the security lock (if applicable) removed.