Yes, you can use your accrued royalty credit when you pay for a new release. You will then be given the choice whether or not to deduct that credit from the total price. If your royalty credit is not sufficient to pay the total amount, simply pay the rest via PayPal or credit card.
Have we agreed that you will receive an invoice afterwards and pay by bank? In that case, too, we can deduct your outstanding royalty credit from the distribution costs of your new release (s). Then report in advance by mail that you want to use this option.