Well, first, BFD2 is now London, and the old BFD2 content isn’t usable. You’re going to have to download it again. @BFD_Drew will have to issue you a new license that you can add to your inMusic account. From there, you’ll redownload it. You’ll need to PM him your old BFD2 serial number.
It’s a Mac, so don’t worry about an uninstaller. Just take the old application and move it to Trash. Also, you might want to delete your ~/Library/Application Support/BFD Drums, ~/Library/Application Support/com.inmusicbrands.softwareunlock, and the /Library/Application Support/BFD Drums directories. That’s where all the action is anyway. Just put them in Trash, or move them somewhere else if you feel unsure about that. Then do a bare bones reinstall.