Update a Single Event
From the Booking Summary:
Click the Event you wish to update
Select the Status from the dropdown
Select Save
Batch Update Multiple Events
Use the checkbox to select the Events you'd like to update
Click Batch Actions
Click Update
Click Status
Select the new Status
Click Apply
Additional Information
If the overarching Booking status is changing, not a specific Event within the Booking, you should change the Booking Status. This will prompt you to update all associated Events at the same time.