In iTunes, go to the tune you think is duplicated. Then right click and select find file in windows explorer. (Usually the are in iTunes/iTunes Music folder) If there are, indeed 2 copies there you could delete one, but be careful not to empty your recycle bin until you check all is well. Usually if you right click a tune there is an option to delete it, then another message asks if you want to send it to the recycle bin or just remove it from the library but keep it in the above folder.No need to drag from playlist to main library - if you delete in the playlist it stays in the library. You only completely delete from the "Music" list. Drag To a playlist, yes.