If it is the Breakout you go into settings and go into security privacy or storage and look for factory reset. If it is just one of the basic pantech phone go into menu the settings and tools then phone settings then security the reset default. It will ask for a code the default code will be the last four of the phone number.
If it is a non smart phone, press OK to go to your menu , scroll to where it says Settings and tools, ---- after this go down to Phone settings then security. The phone will prompt you for a passcode (last 4 of your phone number). The last step should be to hit RESET PHONE