As far as I can tell, there's no way to do this. There really should be.
I'm just trying to replace photos I've previously uploaded with better ones. But what if someone made a mistake and really uploaded the wrong photo for an individual? There seems to be no way to fix that. Suppose a family member objects - no way to delete it. Suppose there's a copyright issue - no way to delete it.
I really think this needs to be fixed.