1. While in a particular service you wish to clear recurrences for, select Scheduling tab and choose Clear Recurrences.
2. Select the desired recurrence you are looking to clear and the date range. Select Clear All.
Once you have cleared the recurrence from your schedule you may want to hide this old recurrence rule from your list to minimize confusion. Feel free to select 'Hide from list' to accomplish this.
Note: read "How do I delete a recurrence" to see how you can also delete recurrences from the calendar view.