Current Contributors
  Displays a list of the contributors currently associated with this media document. Click the Role link to change the contributor's role. Check the 'Delete' checkbox and the contributor will be disassociated from the media document when you save.
Search
  Search remaining (unassociated) contributors by last name.
Choose Contributors
  Displays the list of contributors matching the search. Click the 'Associate' link to associate a contributor to the media document.

When finished, click Save.