There can be different approaches to clean up duplicate files.
When each and every song has basic tags present for at least the title and artist, and are all scanned, imported, and visible in your MusicBee library, as vincent said, you can do a lot from within the MusicBee duplicates feature.
If lots of music files are really scattered around your drives, and are not all properly tagged, and/or not successfully imported in your MusicBee library, you could use external duplicate finder tools to do the job.
That could still be a lot of work though.
Songs with the exact same artist/title could still be different versions. (different recording, live version, etc.)
Files that have different file sizes could still be the exact same song. (different album art, different encoder used, etc.)
If you want to try external tools, here are a few mentioned: http://www.techsupportalert.com/best-free-duplicate-file-remover.htm
(I remember in the past trying a few out, and preferring the one from digitalvolcano)