Press the learn more button arrow in the link I gave above.
Quote: In manual mode, you can delete songs from your iPod without deleting them from iTunes. Make sure your iPod is selected in the Source menu, and then choose the song you wish to delete in the main window. Press the Delete key on your keyboard and the song will be removed from the iPod. To delete multiple songs at once hold down the Command key on the Mac (or Shift key on your PC), select the songs, album, artist, or entire genres you want to delete, and then press Delete.