How to delete repeating events / a whole series
To delete a whole series, go to the event, press the 3 dots ("more") then Cancel > Cancel this and all future occurrences > Delete
The event will be removed from the event list and nobody will be notified. Attendance history for the event will also be deleted.
You can also chose to "cancel and notify the recipients", then delete the event afterwards by going to the "more" tab again and select "delete".
PS! When an event is deleted, it's deleted for the whole group and can not be restored.