Want to delete an Attachment

I'm still working through understanding Service Desk 7.7.1.  I added an attachment to a change.  Now I want to delete that attachment - and I can't.  I can delete the file that is referenced for the attachment, but not the attachment from the change.  I noticed the business object for attachment has Deletion Type = No deletion.  Is this what governs whether an attachment can be deleted?  If so, how can I modify this - it is greyed out in Modify Business Object?  If not, how can I delete an attachment from a change?