You can update your credit card by visiting your account page. 

To find this please be sure you are logged into your account. You can log in here: https://herbarium.theherbalacademy.com/login/

Then click on 'My Account' in the top right corner. On the 'My Account' Page, look for the Subscriptions section. Within this section please locate "update billing details". Click this to update your credit card.