You need to switch to list view to reorder songs in a playlist. To switch to list view click the list view button in the upper left hand side of the top of the iTunes windows:

![List view][1]

Once you've switch to list view you can drag tracks around in the playlist to reorder them. For example, I switch Planet Earth and The Valley in the playlist shown above by clicking on Planet Earth and dragging it up above The Valley and then releasing my mouse button:

![Switched songs][2]


  [1]: https://i.sstatic.net/wnM5x.png
  [2]: https://i.sstatic.net/3D9fj.png