Need to change the factory keyless entry code

My girlfriend has a 2002 Expedition XLT. She always just used the factory keyless entry code. The problem is her ex-boyfriend knows the factory code. Is there a way to change the factory keyless code (even if I have to go to a dealership) or possibly replace the module with a new one?

Thank you in advance for your help.

I know it has been a little while but did you ever get it? I just bought one and there is a factory reset code printed under the dash. a five digit number on a case under steering wheel.