Changing the joint in the drive shaft ?

If I run into a bugger that won't budge I use a big hammer to help start it moving. Then I run a file gently around the yoke ears and start one cap. I push the u joint through the yoke into that cap so the bearings don't move, and while holding them together "tap" the cap through the yoke with a hammer to the other side. Through enough so you can put the opposite cap on and push the u joint firmly into that cap so again you don't disrupt the bearings. Then gently tap it back to center and install the clips.
If after you install the new u joint it seems stiff (not frozen as then it's in crooked) give it a good whack on the yoke and that usually frees things up for me.
Good luck!