The following payment types can be changed for you by our customer service in retrospect: Prepayment and cash on delivery.
For security reasons, we are unfortunately unable to modify any other payment type.
Should you need to make a change anyway, then we can cancel the current order for you, so that you can create a new order with the payment type of your choice. Please contact our customer service.
Any payments received will then be refunded to you (see also When do I get my reimbursement in case of an order cancellation or return?).