As the organizer, open your event and use its edit options to update the details. Check the date, time, length, room, and invitations before saving.
Tell your guests
The event details update in Here. If the change is close to the start, send your friends a message too so they know to check the new plan.
Cancel the event
Use the event's Cancel action if it is no longer happening. Let invited friends know, especially if they already added it to a calendar.
What about a calendar copy?
Check any calendar copy after changes or cancellation. A downloaded calendar file may need to be updated manually.