What we've learned so far will help you delete a song from iTunes if you're viewing your entire library. If, however, you're viewing a playlist and you want to delete a song from inside the playlist, the process is a little different.
Normally, following the previous steps to delete a song from within a playlist only removes that song from the list, not from your computer.
If however, you want to permanently delete a song while in the playlist view, select the song or songs you want to delete and hold down the Option + Command + Delete buttons at the same time (on a Mac) or Option + Control + Delete (on a PC).
You'll get the same pop-up window asking you to decide what to do with the file. Make your choice and the song will be deleted from both the playlist and your hard drive.