You can delete a rating 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. Then click the booking whose rating you want to delete. Under the feedback section, click the delete button to delete your rating.
Note that you have 14 days after the end of a booking to delete your rating. After this rating period has passed, you can no longer delete it.
The instructor will receive a notification when you delete your rating.
If you want to learn more about editing a rating, then please read this article.