Unreceived lines - Correction

We have a vendor that required 10% down. This was entered as an advance billing. Then we got the final invoice which was paid before the shipment was received. It was keyed as unreceived lines. Now that the shipment has been received, the quantities don’t match exactly for me to match the invoice to the receipts. This was due to being billed in kg. I converted this into lbs but receiving converted it slightly different. How can I reverse the original invoice out of unreceived lines and then rekey it correctly? Or is there a way to clear the unreceived lines to the receipts when they don’t match exactly? I tried to put in a debit memo and then rekey but the prepaid deposit is throwing me off. Suggestions?