To update your payment information for your GoComics.com, please go to www.gocomics.com and log in with your email and password.
On the next screen, click on "My Account." Then scroll down to "Subscription", here you will see options to the effect of "Change Plan & Billing Info."
*Please be advised, that if you are simply updating your billing information, you will not receive any kind of "receipt." You will not be charged until the specified date for your future renewal, at which time you WILL receive a receipt.
If your membership plan is already expired, you will see a prompt to upgrade as in the example below: