you will need a hammer, two flat blade screwdrivers, a socket the same size as then end of the uni joint.
you need to take the whole shaft out, both halves.
the two screwdrivers are used to remove the C clip that is on each leg of the u-joint. hold one on each side of the C clip and hit one of them with the hammer. its awkward, but it can be done.
now you sit the socket one the ground and the uni joint on top of it, taking care to align the socket with the cap of the u-joint
hit the yoke between the welded area and the cap. the caps should start to come loose.
getting them back together is a little more difficult. first you take off two opposite caps, put the new u-joint into the yoke then place the caps back on. tap them gently with the hammer. they will go back into place. fiddly job but this is how i do it, and have done many, many times. remember to put the c clips on. do NOT leave them out.
cheers
Jason