This is how I changed my starter on my 5.4.. It should basically be the same...
Jack and support the front of the truck and take the front passenger wheel off.
Disconnect the battery cables. (good time to clean and inspect both of them anyway). Give the posts and cable ends a good scrubbing to ruffen up the surfaces.
Remove the wires going to the starter. Get a good mental image of which ones goes where. It should be obvious, but stranger things have happened...
There are 3 bolts holding the starter in place. 2 you can get from the bottom and the last is on top and you get to it the easiest thru the front wheel well (hence, removing the tire).
You will need a varity of extensions and sockets to get them out. I'm sorry, but I don't recall what size socket they took... It's metric, I'm pretty sure..
The old starter should just come out with a little bit of fudging around.
Take it in to the auto parts store and have them test it first... You will also need to give it to them to avoid paying a 'core' charge when / if you get a new one. If you need a new one, compare the old one to it before leaving the store...
Install in the reverse order of removing. You should only start the lower bolts. Keep them loose and then do the top one. Tighten all the bolts and then attach the wires.
Hook up battery and keep your fingers crossed that you didn't leave something loose or wired wrong and see if you see any smoke or smell burning!
Try to start the truck.
Hopefully, all you have to do is put the tire back on and clean up at this point!
Good luck! I've replace starters ever since I was a kid, so I might have not covered every single step, but I learned by just doing it, so there you go!