Wipe your device: Erase your personal information on the device such as messages, email, calendar, preferences, etc.? Use Options > Security > Security Wipe. This can leave some third party application data on the device.
To 'completely erase' the device software, use JL_Cmder or BBSAK, which effectively is akin to formatting a hard drive on a PC. Then, reload the OS. This will be like having a fresh new out of the box BlackBerry.
Finally, you can use the 'resettofactory' function also, in JL_Cmder or BBSAK. How do I wipe the BlackBerry using Jl Cmder? - BlackBerryFAQ
BBSAK: BlackBerry Swiss Army Knife