These docs are for an old release.
Info on upgrading to v4
updateEvent
Changes data for a single event, rerendering the event.
.fullCalendar( ‘updateEvent’, event )
event must be the original Event Object for an event, not merely a reconstructed object. The original Event Object can obtained by callbacks such as eventClick, or by the clientEvents method.
Here is how you might update an event after a click:
$('#calendar').fullCalendar({
eventClick: function(event, element) {
event.title = "CLICKED!";
$('#calendar').fullCalendar('updateEvent', event);
}
});