Changing your card details
If you want to use a different payment card to a previously saved version you can change it in the payment popup during the checkout process -
If your payment was made via Stripe -
Click next to the 4 last digits of your card number (obscured above, but they will be visible on your screen). Then click on backspace or delete on your keyboard to clear the saved details. Enter your new details, then click the pay button.
Other payment provider types may have a slightly different interface for changing card details. You should always look for your credit/debit card number and click on that (or an icon nearby) to make a change.