The previous post is great and gives the correct way to do the job...however, if you want to make it easy just take an open end wrench bigger then the shaft and rest it up under the shifter knob. Take a hammer (preferably a rubber/plastic mallet) and give the underside of the wrench a few good whacks. The knob will slide off the top of the shaft. You will want to have your hand over the engage button as it will fly off and mach 5 if you’re not ready. A great idea I read (and tried) was to put a plastic baggy over the top to catch the button and spring. Also you will have to disconnect the overdrive switch from the side first.
when its time to put the knob and button assembly back on, connect the overdrive button, position the knob in place and tap the assembly back on top of the shaft with the mallet. You want it to all sit firmly back in place with no play at all, otherwise the button will fly off while you’re driving down the road at the most awkward time...usually going 70 mph down the highway, or going in reverse down your brother-in-laws steep driveway.

Have fun
Ryan Rice