Update

<script>
  var dataSource = new kendo.data.GanttDataSource({
    data: [
      {
        id: 1,
        orderId: 0,
        parentId: null,
        title: "Task1",
        summary: true,
        start: new Date("2014/6/17 9:00"),
        end: new Date("2014/6/17 11:00")
      }
    ]
  });

  dataSource.fetch();

  var task = dataSource.at(0);
  dataSource.update(task, { title: "New Title" });

  document.write(task.title); // outputs "New Title"
/* The result can be observed in the DevTools(F12) console of the browser. */
  console.log(task.title); // outputs "New Title"
</script>