Click the client portal will bring you to a log in area :

Upon logging in you will then select the my details page 

In the top left you will select change my credit card details :

You might see some contact/billing information here, which you can change if needed. You will want to enter in your new CC details here :

You will hit submit, and then retry your payment. If you have any issues, please email us : support@madgenius.com