If you need to change the credit card that you're using to pay for your Thinkific plan, just log into your account and select Account details under your account.
Your account details will come up showing your current payment plan with Thinkific. From here, you will want to click on the Update Credit Card button.
Enter your new credit card details into the new page that appears, and hit the green Update and Save button!
And that is it! You've now updated your credit card and it will take effect on the next billing cycle.
Click here for info on updating your billing email address.