The databases, settings, and artwork live in the /Users/USERNAME/Library/Roon folder.
To get there:
- Open Finder and click Go in the top bar
- Hold down the Alt key to unhide the Library folder
- Click the Library folder
- Find and delete (or rename) the Roon folder
Depending on how you configured Roon, there might also be a /Users/USERNAME/Music/Roon folder.
Also, just drag the Roon or Roon Server application to the trash.
If you delete those folders you should be all set!
Cheers, Greg