You can update your billing information at any time within your online account at account.gradguard.com
Just select your name in the top right and click "Account Settings."
Once you do so, select "billing" then choose if you need to edit the card information for your renters policy or your tuition plan and click "Edit."
That's it! Make sure to save your updated card and details. Note that you can only edit the billing information if you are the account holder of the policy that has been purchased.