Log in at Tayst.com. Click on "Manage" and scroll down to "Billing Details". From there you will be able to update your form of payment and/or your billing address.
Once you select "Billing Details" from the drop down menu you will then click on "Payment Methods"
You can either click on "Edit" to update the current information on file, or you can click on "Change Payment Method", and from there you can update your payment/billing information.