I've never replaced them but it doesn't look hard. (Looking in the manual) The door panel needs to come off http://www.lexls.com/tutorials/body/fdoorpanel.html
Then take off the top trim on the door. There's 2 clips on the rear part of the trim, 1 in the center, 1 towards the top. Then pull trim upwards. There's 17 clips on the lower portion of the weatherstripping, none on top. (The trim holds the top in) The rear door is pretty much the same as the front except the door panel has 7 clips and 3 screws, upper door trim has the same 2 clips but has 1 screw in the front, and the weatherstripping has 18 clips. You might want to get new clips for the weatherstripping or it might not seal right.
Hope that helps ya out.