How to remove duplicated demo content?

I have a couple demos and wanted to try each one. When I imported the second demo it just imported the content over the first demo that I tried before. Now i have a long list of duplicated menu items and etc.
How to remove duplicated demo content?
How to switch between the demos? Should I install separate websites for each demo and then import only one per website? Or is there a way to remove current demo and import another one?