Not hard to do, don't worry.
Buy a quality replacement, Hardy Spicer etc, not expensive, £5 or so.
Using a 9/16 spanner or a prop bolt removal tool from
www.difflock.com (about £10 but worth every penny) loosen all four bolts on the end of the prop with the knackered UJ. Remove them, drop the prop flange down and pull it off the other part of the prop that is still attached to the car. Separation occurs at the sliding joint.
Four circlips retain the bearing caps in the prop, remove these (Inside circlips), then using an appropriate drift (socket) and a vice or two bits of wood for support underneath, give the bearing cap you choose a good whack. The other side will move outwards and with a bit of persuasion you can grip it with grips/vice/pliers and twist it out.
Do the same to one of the caps at 90 degrees to the first one you whacked.
You can now move the yoke inside the joint freely, whack the other bearing caps out or through and your done.
Rebuilding it is the reverse of stripping but I prefer to squeeze the new caps in with a vice rather than drifting them in.
Don't forget to fit the nipple to your new UJ if it isn't already fitted and put a good blob of grease in each cap before inserting the yoke.
That's about it but if you want more detail, search in the technical archive at this site:
http://forums.lr4x4.com/Its a treasure trove of knowledge.
Stu.