The shift knob on your car should look something like the above (probably all leather with a plastic black piece at the bottom instead of chrome)
To remove just the knob, twist the black plastic piece on the bottom (chrome in the pic above) clockwise (when looking from the top) about 1/2 turn and then push it down (off the knob). The knob should pull up/off now.
Install is reverse, put the bottom plastic (or chrome) piece on first, slide the new knob on, and push the plastic/chrome piece up on to the knob and twist about 1/2 counter clockwise.