Tap the event to open its editing screen. Tap "Delete", and when the confirmation "Delete this event?" appears, go ahead and delete it.
You can also touch and hold an event on the calendar and select "Delete".
For repeating events, choose either "Delete This Event Only" or "Delete All Future Events".
In the event list on the calendar screen, you can also delete an event by swiping it. This is the easiest way to delete events.