After you have paid, you can cancel a class and receive a credit. You may cancel any class up to an hour before.

1. Log in.
2. Click or tap My Registrations ▽ , then click or tap the link to your course.
3. Scroll below the calendar of your course page.

1 credit will be added in your  My Registrations ▽  section.

Also see:

How to use a credit for a replacement class