Currently, the best way to manage your payment methods is at checkout. If you already have a cart full of items, you can head straight to checkout. Otherwise, add a single item to your cart (don't worry, you don't need to pay for it!)
Once you're at checkout, select "Payment Methods". Here, you can see which cards are already on file, and add a new one.
After adding a new card, this will be available for all future purchases. If you need us to switch the card attached to a previous order or membership, feel free to send us a message and we'll switch it over for you.