heater stuck

I have a 1997 e 150 that is only blowing hot air out of the front (rear air works fine). i found a thread that talked about the door bomin stuck and a tsa issued by ford. does anybody know how hard this is to do at home and if not how much this would cost.
thanks

Hi, My local repair shop wanted 800.00 to fix my heater door. They said because they would have to remove the dash board and it's a big job. I'm going to fix mine myself before I will pay anybody 800 dollars.

Bob