If you need to update your payment information, go to Midnightpulp.com and log-in to your account. Once you are logged in, click your name on the upper right of the homepage. Then click "Account" in the drop-down list. Once on your Account page, click the "Subscription" tab.
Click "Update Payment Method," and you will see the prompts to enter your new billing information.
Make sure to click "Update" and you're all set!