You can delete lessons by going to the calendar, clicking on an event and then clicking on the "Delete" option in the pop-up bubble. You will then have the option of deleting the current event, the current event and all future events or all events in the series.
It's highly recommended that you do not delete past events since this will also delete the related lesson records and cost, which can impact your financial and billing information.
Select the deletion option you would like to use and click "Save".
Upon successful deletion you will be redirected back to the calendar.