You can delete a class topic from your studio by clicking the "Edit" button next to a class on your Classes Tab. Scroll to the bottom of the page to click the delete class link. (See image below)
In order to delete a class, you must first ensure that all upcoming class times have been cancelled, that no one is signed up for a future instance of the class, and that the class is not part of an existing package.
Please see the following relevant articles:
If you think that you may come back to the class topic at another time- you can also Hide A Class.