How do I reprogram the car door keyless entry pad of my 2005 Lincoln Aviator?

I have the original code from the factory. Just want to change it to a new one.Directions to add an alternate code to your keyless entry system are explained in detail starting on page 166 of this digital owners manual:

http://www.motorcraftservice.com/pubs/content/~WO5231/~MUS~LEN/34/05231og3e.pdf

note:
The above link is to download your complete owners manual.
It is a free download courtesy of Fords website & it is in pdf format so it can easily be saved to your computer for future reference.
I hope this helps.