Renewing all the locks on an 1993 Ford Escort?

I have been looking at replacing all the locks on my 1993 Ford Escort XR3i, I think i can remember how to do the doors & ignition. The fuel filler cap is the only thing that is giving me cause for concern, any ideas how i get the old lock out of the cap. So i can put the new 1 in?

Tachewing
March 2009