You need to remove the 'staked' metal on one of the bearing caps , on each of the 'yokes' .
Take a socket larger than the diameter of the bearing cap, place the open side of the socket against the 'yoke', place another socket slightly smaller in diameter, so it fits up against the cap .
Place in your press, add pressure, and both bearing caps should start to move, when the caps are free of the yoke, the cap that went into the open side of the socket should come off of the u-joint .
The opposite end cap should be free of the 'yoke', then you should be able to remove that side of the u-joint .
Repeat the process on the remaining caps on the other yoke .
Installation of the new u-joint, is just doing these steps in reverse, make sure you lube the caps up before attempting re-installation .
You may have to remove all of the 'staked' metal, depending on the dimensional differences between the old u-joint, and your replacement u-joint .
All you need is a chisel, or other such tool to stake the new bearing caps .
Hope this may have helped you understand the process a bit better .
Kinda use the same process to remove the needle bearings from the rocker arms .