To remove a class, first go to your Admin page and select the class you wish to delete from the Classes tab.
Click Class Settings in the upper right corner.
On the Class Settings page, scroll down and click "Additional Settings." When the additional settings options appear, click Cancel Class. This will not only delete the class, but all the students registered to that class.
The class won't disappear immediately, in order to allow a teacher one week to cancel the request. (This is a safety measure to prevent the wrong class or students being deleted by mistake.)