12/1/16: Update: You may delete orders within 15 minutes of placing the order. You may also delete orders that are on hold. This goes for single product or multiple product orders.
There is no way to delete orders unless they are on hold.
If you have funds in your account, and you order product, we start making it right away. We print postage sometimes within 1 hour to give you time to fix the address.
However, since we make product right away, we don't allow you to delete any orders unless they are on hold. When an order is on hold, we have not yet made anything.
What you should do is to submit your orders, make any modifications and/or deletes, then pay the bill.