The Delete Class... menu item deletes one or more classes
  from a library. The class must be empty or CMS will not
  delete the class.

  When you choose Delete Class..., a dialog box appears,
  allowing you to specify options for the class you are
  deleting.

  To determine which generations belong to a class, do the
  following:

  1. Click on a class.
  2. Pull down the View menu.
  3. Choose the Expand submenu.
  4. Choose the Children menu item.