Your approach will be different, depending on whether you are just changing instructors, deleting one class time, or not offering a particular class anymore. Here are your options:
Delete or Cancel One Class Incidence
If you want to cancel an upcoming incidence of a class, you can go into that class time (click the green "Classes" button at the top of your page) & delete it as long as no one has registered for it in advance.
If you need to cancel multiple classes, you can do that & share a special notice with your customers about it. Click here to learn how.
You can't actually delete a class that has any reservation history associated with it. However, you can mark it as canceled.
You can do either right from the calendar view...
Or you can go into the individual class time to delete it (or click Edit Class for the option to cancel):
Delete a Recurring Class Time
To remove a recurring class from your schedule, go to Manage Account => Manage Classes & click on the class name to "Manage The Schedule For This Class".
From there, you can delete the recurring class.
Delete or Archive a Class Type
If you actually don't offer a particular class type anymore, you can archive it via Manage Account => Manage Classes.
From there, you can select the class description you no longer offer & "Edit the Class"
Archive it here and so it doesn't appear in your active class views anymore. The history for the class will still exist for reporting purposes. You can only delete a class type that has no history.