You will need a chain whip, the freewheel tool, and an adjustable wrench. Assuming you have the wrench, you'll save money over paying a shop if you do this twice. It is not particularly difficult. While things will generally line up well, I would also always check the rear derailleur adjustment any time I replaced the cassette. If you replace the cassette and you still get skipping, you need to replace your other chainrings. For recent components, these often need to be pretty specifically matched to the make and model of your crankset. The tooling to change this is pretty simple--a chainring nut tool, and allen wrenches in most cases.