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 higher or lower position in the list.
Notes
You can also use the Playlist pane in Now Playing to add to or adjust 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.
In Media Library, when a playlist is selected, a playlist menu icon is displayed at the bottom of the screen in the Media Information pane. You can click the icon to display a playlist menu which contains the following commands, EditPlaylist, DeleteSelected, Clear, Sort, Open, SaveAs, and CopytoCDorDevice. The playlist menu icon is also available in Now Playing.