A master reset will return the handset to the default factory settings and erase all personal information on the handset.
This type of reset should be used as a last resort to fix major errors, and all important information should be backed up before proceeding.
From the home screen, tap the Menu key.
Scroll to and tap Privacy.
Tap Factory data reset.
Read the warning and tap Reset phone.
Tap Erase everything.
The handset will restart and reset to factory settings.