You don't need to remove the knob to replace the push button.

Simply pry out the old button with a small, thin screw driver....try not to damage the knob...the button just pops in.

There is a spring that pushes the knob up, so be ready to catch it.

As far as removing the knob.

First, loosen the plastic cover from around the shift lever so that you can lift it up and access the wiring underneath.

Remove the push button.

Lift the plastic cover up and feed enough slack in the OD wire so that you can pry out and un-plug the OD button.

Pull the OD wire out of it's hole and run it out the big hole in the top of the shifter knob....This will prevent you damaging the wire when you pull the knob.

Removing the knob is as simple (or as hard) as pulling up on it hard enough to pull it off of the shift lever.
It is held in place by plastic clips molded into the knob that fit into a groove on the shaft. Usually these clips are damaged when you pull the knob, so don't remove it unless you have to, and be prepared to but a new knob if you do.

Hope this helps
steve