When reinstalling Ghost, what happens to previous instance?

Hello, I am trying to reinstall ghost in order to upgrade to v5 since my old version did not have SQL 8. When I read the document on how to do this, it says to simply follow the same process as installing Ghost (i.e., create a new user on Ubuntu, run the process, etc). My question is–what happens to the old installation of ghost? Will the new installation just automatically work if the old one is still around?