Most times the disposal is not broken but just jammed with stuff. So check out my video on troubleshooting disposals before you buy a new one. It could save you a lot of time and money. But if you do have to replace it, just remember to have the power off and don’t forget the knockout plug. Other than that you should have no trouble. It can get a bit tricky if you are buying a different model that has different connections. You may need to move a few pipes around or at least tweak them. Hopefully you have the info and courage you need to take this on yourself.
The disposal I am installing in this video is a Badger 1 made by insinkerator. It’s only 1/3hp.