To edit a single instance of an already scheduled recurring event:
1) Hover your mouse over the appointment and right-click
2) Select Edit Instance
3) Edit the instance and click the Save button
Note: All other instances will be preserved.
To edit all instances of a recurring event:
1) Right-click on the event and select Edit Event or double-click on the event
2) Click the Edit button found in the tools menu at the top of the window
3) Edit the instance and click the Save button
If you're editing the instance you can also at that time see the details, attendees, recurrences of the events and any possible attachments and modify accordingly.
