The instructions that come with it are pretty good.
Turn off the circuit breaker to the thing. If it is plugged in, just pull it out. If it is wired in, then you'll need to disconnect it. If the wire is long enough, don't worry much, do it later. If the thing plugs in, you'll need to move that cord to the new one. If it is in good shape, that is. If the insulation is cracking because it is really old, you'll nedd a new cord. If it is wired in, as long as the wire insulation is in good shape, you can reconnect it.
The outlet is held in by a single screw that holds the flange. Take that off. The plastic part of the elbow will come out of the piece going to the wall if you loosen the nut and then you can slide it out. It will be easier to do that after you remove the thing, but take it out if you can, if not, don't worry about it.
If you have a dishwasher hose connected to the thing, loosen the clamp (might be a screw clamp or a spring clamp) and pull off the hose.
There is a ring up around the bottom of the sink that has tubular sections around it. This attaches to a cam-lock that actually holds the thing to the sink. Using the allen wrench as a handle (it should fit into the hole of the tubular fitting), turn it about 1/8th turn and it will release the thing; careful, since it will fall down at this point if you aren't holding it.
If you are going to replace the part in the sink (you don't have to - buff it up with some steel wool and it will look as good as a new one after a week), then you need to remove the nut, use plumbers putty under the new one, then install it. There are some good pictures in the manual.
Once you have the thing down on the floor, remove the screws for the wiring access and undo the wire nuts. Replace the wiring into the new one matching up the colors.
Read the manual, and see if you can follow it.
Note, if you have a dishwasher hooked up to the thing, you'll need to knock out the plug on the new one before you connect it up. It is probably eaiser to do this before you install it. Take a heavy screw driver...put it into the hole for the dishwasher connection, and hit the screwdriver with a hammer to knock out the plug. Tip the thing over to empty the plug, it should fall out.
In most of those I've replaced, I just leave the original drain in. If you have a real odd one, the new one won't fit, but it is rare from my limited experience. As opposed to a pro, I've only replaced maybe a half dozen - most of them have probably replaced hundreds if not thousands. It usually only takes a half-hour or so, but plan for more on your first one.