You can delete classes several ways and it will depend on how you are using the service (ie. through the web browser or on a mobile device).
(iPhone, iPad, iPod, etc.)
On any iOS device you can simply swipe the class you wish to delete by swiping to the left and uncovering the ‘Delete’ button. Tap Delete to finish.
(Samsung Galaxy, Google Nexus, etc.)
On Android devices you can simply swipe left or right to bring up the ‘x’ option. Tap the ‘x’ to finish.
(Any computer/laptop/tablet that allows you to go online.)
To delete Classes in the Browser version you simply click on the radio button to the right of the class and then click on the ‘Delete Class’ tab above.