1) Remove driveshaft. It's a good idea to have new straps and screws for reinstallation, but get new screws at the very least (should be able to use 1/4"-28 x 1" socket head capscrews - that's what I use. They're cheap insurance, and socket heads have a reduced head to fit, wrench internally, and are heat-treated to SAE8 specs anyhow.)
2) Remove seal. A seal puller would help, but a flat screwdriver will also do the job.
3) Clean the seal seat. A little carburettor cleaner and a clean rag should be enough - you just don't want anything in there that will gouge the aluminum.
4) Install the new seal. Since the output sticks out just slightly, you might find it useful to use a small bit of pipe or a pipe fitting (either with a plug in the end) or a large socket to press the seal rim all at once. Make sure that whatever you use bears on the metal part of the seal! No, I don't recall what size you'll need... Tap gently with a hammer until the seal is fully seated, and I find it useful to smear a bit of RTV Black over the outside of the seal - where metal seats against metal (again, cheap insurance.)
5) Inspect the slip yoke, and clean if necessary. I'll usually give it a pass with some 400-grit emery cloth, just for cheap insurance. Wrap it around the sealing surface, and turn a couple of times. This removes surface rust and other yock. Wipe clean with carburettor cleaner and a clean rag again to remove grit that could compromise the seal.
6) Lightly grease the slip yoke and install.
7) Reinstall the aft end of the driveshaft, using new screws (at a minimum!) and new straps (a good idea.) Use LocTite 242 on the screws to hold them in place - few things are more purely irritating than losing a driveshaft at speed...
Since you'll have the driveshaft out, this is a good time to think about changing the U-joints as well - since half of the job is already done... In any case, get out your grease gun and lube everything while you're down there - five U-joints in the two driveshafts, the two U-joints behind the wheels, the ball joints, and all the tie rod ends and such. Gives you a good chance to check it all anyhow.
The job itself is simple - if you take an hour to do it - with lubricating everything - I'd be surprised. Add a half-hour if you have to change the two universal joints in the rear driveshaft (which probably need it anyhow.) This is also a good opportunity to change the fluid in your transfer case, since you'll lose some anyhow. Dexron II/IIE/III will work - same stuff you'd use in the AW4 (your automatic.)