Once an order has been placed, you won't be able to make changes to the item. Your only option would be to request a cancellation of the order.
Important Note: if your order contains multiple items, ensure you've submitted a cancellation request for each item you want to cancel.
You can request to cancel your order as long as the order has not yet shipped. To do so, log into your account, locate the item in question under My orders and click Help.
From there, click I want to cancel my order and then pick the relevant reason from the drop down, enter the details and submit your request.
Your request will be immediately sent to the vendor, who will then need to confirm or reject the cancellation based on the status of the order on their end.
If the cancellation is confirmed, a refund will be initiated to your original form of payment and should post in the next 3-5 business days, depending on your bank.
If the cancellation is rejected, the order will proceed as normal and you're welcome to return the device once it arrives for a full refund. You can find more information on opening a return request here.