If you receive a supplier invoice or additional landed costs after you have received the stock in on a PO, you can update the pricing as required before you send it through to accounting.
Open the received PO and click on the Update Invoice Details button.
The following screen will let you update the invoice dates, supplier invoice number, invoice pricing and landed costs as per the suppliers invoice.
Note you cannot update the PO details, received date and product quantity. This is important as it is assuming you have received the stock numbers in correctly form the shipment/delivery. Save to apply the figures to the PO.