The "U" shaped pin in the front of the knob pulls out, then all you do is pull the knob off of the base. If you want to put it back in, squeeze the U-shaped pin so that the pegs are paralell (kinda hard, it took me 15 min) and slip it back in place.
What kind of knob are you getting to replace it?
I went to Pep Boys and got a Carbon Fiber T-bar, the one with the three hex head screws on the botom. It was to big on the shaft and wiggled everywhere so I took it off, and wraped electrical tape around the shaft. I just went till I barley fit the handle over the tape and then just hit it on with my fist and screwed the screws down. Just make sure the handle works right before you tighten. If it doesn't, hit it down further and then tighten.