You have to cancel an event before you can delete it.

1. Click in the left sidebar on Events and then on the For organisers tab.
2. Click More next to the event in question and a dropdown menu will open.
3. Select Cancel.
4. In the Message to participants window you can let those people already invited know the reasons for cancelling.
5. The event will be deleted and the message sent out as soon as you click Send.

Please note: It isn’t possible to cancel an event that has already begun.