You can manage your bookings by going to your booking page. If you are also an instructor, make sure that you click the customer toggle to see all your bookings as a customer. Now, click on the booking you want to view.
Here you can see all the information about the booking as well as edit it, contact your instructor and edit the rating.
To cancel, click the cancel button shown below the side bar on the right of the page or after clicking the See details button on mobile devices.
You will receive a full refund if still within the free cancellation period. Afterwards, you will receive a partial refund. Learn more.
Note that the instructor receives a notification when you update the booking.