How do you replace Jeep Liberty Sport 2002 door keys?

If you have proof of ownership (title, registration, etc) and the VIN number (which should be on said documents) you can go to the dealership and they can look up your key code and cut you new keys.

Your liberty uses a transponder key so the dealer will also have to program the transponder, I haven't dealt with Liberties so I am unsure on whether they can program the transponder without the vehicle present.

I suggest calling the parts department of your local Jeep dealer and talking to someone there.