To cancel a single event, go to the event and press the three dots in the menu, then 'Cancel event' and a 'Cancel and notify recipients'. The event will be marked as cancelled in the event list.

To delete a single event, go to the event and press the three dots in the menu, then 'Cancel event' and 'Delete'. The event will be removed from the event list and nobody will be notified. Attendance history for the event will also be deleted.