If you got an auto ignore what comes next.
If its a manual...its slightly more involved than just twisitn it off. The stock shift knob as a silver rectangular trim piece that is attached to the knob. The shift boot in turn is attached to the trim piece with a rubber fastener. The bottom of the boot is attached to the console trim piece. Its easy to pop off the trim piece at the base...that way to can get at the aformentioned rubber fastener. You can then slide the boot downand twist off the knob. Reinstallation of a different knob will take a little rigging to re-attach the boot. I know I'm talking in generalities...so PM if you need details.