Just did this one last weekend. I had the shaft situated horizontally (actually just sitting on a cardboard box). Some earlier posts recommended having a good pair of snapring pliers for the job, so I went out and bought a set. After doing all that, I ended up just using a flat-head screwdriver with a particularly wide head. While holding it hard against the driver (the part of the joint to which the shaft is directly connected), I tapped the driver with a light duty hammer. It probably took a couple dozen tries, but the circlip eventually cleared the groove, and I was able to tap the joint the rest of the way off. In short, what you need is patience and a flat-head. A second pair of hands always helps, too.

To really clean out the joint (and learn how those things work), just angle the driver and cage as far to one side as you can and start removing the ball bearings. It'll come apart (and later go back together) pretty easily.

Have fun.