Turn off you phone.
Press volume up and the power button.
keep on pressing until the logo appears,after logo appeared release volume button &
keep on pressing the power button and u will enter in the recovery mode.
Select the wipe data/factory reset option.(using volum up & down button)
Once you have done the factory reset, you will see a confirmation message.
Press Yes delete all user data option and touch the Home button to confirm it.
Now Select the reboot button and Your phone will reboot in normal mode