1992 Lincoln Town Car Door Locks

I have owned this car for 16 months now and I cannot seem to find the answer to this problem. There is a keypad on both front doors near the door handle where a code can be entered to unlock the doors from the outside. Previous owner says they had the code written down but they never used it and must have misplaced the codes. My question is. Is there an easy way to erase the old codes and enter a new code that will make this feature work? Seems like such a waste not to use them.
Thanks
Tornillo