Click Media Library, and then expand My Playlists to display the playlists.
Click the playlist that you want to modify.
Click the item you want to move, and then click the Move Up or Move Down button.
-or-
Drag an item in the playlist to a different position in the list.
Notes
You can also use the Playlist pane in Now Playing to add to or edit your playlists and to select the order you want your items to play in. On the View menu, point to Now Playing Options, and then click Show Playlist.
When a playlist is selected in Media Library, the Select Playlist Options button is displayed at the bottom of the Details pane. You can click the button to display a menu of playlist options that contains the following commands: EditPlaylist, DeleteSelected, Clear, Sort, Open, SaveAs, and CopytoCDorDevice. The Select Playlist Options button is also available in Now Playing.