Hard Reset (Factory Reset)
If you forget your lock sequence and backup PIN, you will have to perform a hard reset to gain access to your phone.
WARNING!
Performing a hard reset deletes all of your user data, which includes pictures, videos, and music saved to your internal memory. Please make sure to back up your information prior to performing a hard reset.
Turn the power off.
Press and hold the following keys at the same time: Power/Lock Key
+ Volume Down Key 
.Release the keys when the FACTORY HARD RESET screen is displayed.
Press the Power/Lock Key
to continue or the Volume Keys 
to cancel.Press the Power/Lock Key
once more to confirm or the Volume Keys to cancel.