Once the check out process has been completed, changes to the order in terms of item/size/color/quantity can no longer be made. What you can do is cancel your order completely within two (2) hours from the time you placed it so you can place a new one with the changes you want. You can see this on your order confirmation email and on your online store order history.

You also have the option to accept the order upon delivery or pick-up the item in your chosen store and request for a return-exchange instead.