Once your order has been successfully placed, you will not be able to change the payment method.
You may cancel your existing order, and place a new order with your new preferred payment method.
You can find out how to cancel your order here.
*Note: Online cancellation can only be used within 1 hour after the order is created, and the item you want to cancel has not been shipped yet. If you want to cancel the order after 1 hour, please contact Customer Service to request for cancellation.