No you don't need to delete the folders!!! Either within iTunes or another mp3 app. change the id tags. Within iTunes just select the tune on the main playlist, Command (apple key) & i (OR go to iTunes menu choose File>Get Info), & then correct the details of id tags for the artist & album, etc. When you exit that window. You'll find that the tune now has the adjusted name & info. Double-click on that tune & iTunes will make the adjustments to its library by itself. It will move the tune to a new location under the correct artist & album name. And the previous unknown folder will disappear. Likewise if you change the id tags within another mp3 app, then the next time you open iTunes, likewise double-click that tune & iTunes will make the adjustments to its own library. So don't attempt to move/delete files manually in the Finder. Do it properly within iTunes.