You can only edit events you have created, and those you have accepted from accounts such as Microsoft ActiveSync Exchange.
Note: Editing events is not supported for all accounts.
While viewing an event, tap .
Note: If you're editing an event that repeats, you'll be asked whether you want to edit just that occurrence or all occurrences of that event.
Make your changes to the event.
Save. Or tap
Send update if you've invited people to the event.