Unfortunately, once an order has been placed we do not have the option to add, remove, or edit the quantity of any items in your order. Additionally, promotional and discount codes cannot be applied post-order, nor can their effects. However, if you contact our support they may be able to cancel your order so that you can place a new one with the appropriate items.
Note: Orders can only be cancelled if the request is made within a few minutes of the order being placed.