Black Outline Boxes - Can't Delete

I  am trying to edit an existing PDF with Adobe Acrobat Pro DC and it has designated black outline boxes that had text boxes inside them. I'm assuming these got set up when the original document was created.  They had pictures in them and I don't need as many boxes as they had.   I got rid of the text boxes but can't find how to delete the black outline boxes which are showing as blank black boxes on my document.  If anyone knows how, I sure would appreciate the help.