I found this excellent step-by-step procedure for doing the replacement:

http://brandonsprojects.blogspot.com/2008/07/blog-post.html

Two things I'd like to add. The first is that compressed air (in a can if you don't have shop air) is handy to blow clean the switch, mine was filled with fluid. Use eye protection and wrap with a rag so it doesn't splatter everywhere. I further cleaned things up with Radio Shack contact cleaner and blew that dry also.

You also are going to need a 1" crescent wrench, as the shoulder width on the new switch is greater than the 9/16 width of the old switch.

Good idea to make sure you tighten the hell out of the new switch, I didn't and mine leaked a bit...

The signature in my signature takes you to pictures of various repair projects on my '96 Windstar.
I have included pictures that show the brake pressure switch replacement.