For starters, regardless of what your manual may say, use no hammers to extract the bearing cups. Hammering on a yoke will distort it, only making your reassembly job more difficult. If the yokes are distorted, your new bearing cups will likely not seat fully, and the new joints will be stiff.
To get the old cups out, get some sockets and a vice. Place a socket that just fits inside the yoke hole on one side, and on the opposite side, a larger socket that fits on the outer edge of the yoke hole, and will allow the cup to slide out of the yoke. Place all this in the vice together. (you may need an extra set of hands) Then crank the vice. Once the cup is about halfway clear of the yoke, you should be able to pull it the rest of the way out.
Installing new joints is also done with the vice, and a heckuva lot easier. Put the joint in the shaft with one cup off. Push that side through one of the yoke holes and replace the cup on the joint's shaft. Put the circlip in the other yoke hole to provide a stop for the joint.Then place the whole thing in the vice and crank away until the joint is flush with the shaft's yoke hole. Then use the socket that fits inside the yoke hole to push the joint on through until it is flush with the circlip. Install the other circlip. If the joint's cups don't both fit flush against the circlips, it's possible to place shims (made from a soft drink can) between the clip and the cup.
Note that the grease nipple is correctly fit against the yoke's indentation for it. You may find, as I did, that the aftermarket grease nipple won't fit regardless, and you'll need to plug the hole with an allen bolt, or a bolt with the head cut off and a slot hacksawed in the center for a screwdriver.