Most disposers are installed the same way. Turn OFF the breaker to the power circuit (unless it is a plug-in model, if so, unplug it) and disconnect the wiring. Disconnect the drain piping from the disposer by unscrewing the nut holding the pipe to the unit. At this time, if your water supplies are disconnected, you can remove the whole sink, disposer and all. Or, you can also remove the unit from the sink drain basket by turning the connecting nut counter-clockwise. Be careful doing that though as the unit has some weight to it. You may need to tap on the rounded extensions on the nut to break it loose or insert a scewdriver into the holes and turn it. If you have a dishwasher connected directly into the disposer, you need to disconnect the hose also.
If you have never made a mistake, you haven't done much.