How to replace unit in this?

ScottOmatic

You get one of these:



But you are looking at an image of the Bose stereo package, which would be dumb to get if you are just going to go aftermarket anyways. It is much harder to deal with than the base stereo so it'd be a much better idea to get a package with the base head unit, which looks like this:



Apparently you can use the stock faceplate but there may be a slightly larger panel gap around the head unit, you might still want to get the aftermarket one, like posted above.