The Delete Group... menu item deletes one or more groups
  from a library.  The group must be empty, and also cannot
  belong to another group.

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

  To determine the elements and groups that belong to a
  specific group, do the following:

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

  To determine the elements and groups that belong to
  another group, do the following:

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