How do I change out a bathroom vanity cabinet?

First look at the plumbing. Your old vanity may not have a back, therefore making it easier to run plumbing during install. Or, your old vanity may have had holes specifically cut for the plumbing, you will have disconnect the plumbing to remove the vanity.

Either way, if you are removing the vanity, you will have to remove plumbing. Some vanities are connected to the wall with nails/screws and others aren't. Usually the counter top is caulked to the wall, you will need to cut the caulk to make it easier to remove.

You should be able to use a pry bar to remove the vanity top from the vanity and the wall. However, it will be a lot easier if you disconnect the plumbing, cut the caulk on the counter top, and then pry the whole unit from the wall. It may seem like fun to smash the vanity with a sledge, but that generally creates a large mess that you then have to clean up.

After you have removed the old one, installing the new one will be pretty intuitive. You basically attach it to the wall with some form of anchor, a lot of times, screws which are supplied with the new vanity. Reconnect the plumbing. Then caulk the new counter top.

https://www.youtube.com/watch?v=jRXo1ytjF9s

https://www.youtube.com/watch?v=Oq1pkZD7DGo

https://www.diynetwork.com/videos/removing-a-bathroom-vanity-75919

or if it doesn't NEED to be replaced, paint it, put on new hardware, and new faucets.... if the counter is not to your taste, you can either just replace it or put on a new finish -- depending on 'formica', 'tile', etc. .... if the sink it self is not to your liking, you can also use a tub/tile refinishing kit , RUSTOLEUM, 'BATHWORKS' and AQUAFINISH all make tub/tile refinishing kits ...

Before you purchase a new vanity unit, either with an integrated sink, or a separate countertop and sink, be sure that the drain position is the same as the old sink. Otherwise your plumbing underneath the countertop will not match up to, or connect with the new drain.