To change payment method, you need to cancel current and create a new payment.
Canceling existing payment
Log in to your Control Panel and click "Financial Documents" in "Account" panel.
Go to "Unpaid Orders & Invoices" tab and from the list, click the payment of interest.
In "Documents" tab check payment you wish to cancel and click "Cancel" button.
Creating new payment for order
- Click "Financial Documents" in "Account" panel.
- Go to "Unpaid Orders & Invoices".
Check boxes next to document for which you'd like to create new payment and click "Pay Documents".
Chose payment method and click "Next".