You're able to delete any event created by members of your organization. Some events such as holidays and member birthdays are not able to be deleted as these are automatically created by the Greek Chapter system.
To delete an event:
Go to the calendar
Tap on the day with the event you'd like to delete. For multi-day events, this can be any day that contains the event
Once on the day details screen, long press on the event you'd like to delete
A menu will now appear with the option to delete the event
Confirm the deletion of the event and it will be removed for all users