This actually helped, thanks!!!  In case it's unclear to anyone, for some weird reason it seems to matter how you get to the Receive Payment window.  Instead of getting to the Receive Payment window through the + New button, go to Customers and find the customer you're looking for, and go to New Transaction > Payment. That will take you to the same Receive Payment window mentioned earlier.  Then it should work to select the credit memo(s) you want to apply to whatever invoice(s).  The Amount Received and Amount to Credit should be $0.00, while the Amount to Apply should show the total you're applying.