To delete a series from your schedule...
Go to Manage Classes.
Click on the series name & delete any reservations that might be there (you cannot delete classes that have existing reservations).
Once reservations have been deleted, you can delete the series. Click on the Series name, click Edit Series, and you'll see and option to delete....
That will delete the Series - however the original classes that made up the series are still available. Now they simply aren't bundled together in a Series!