Tasks can be moved within a project, most commonly with a drag and drop. Larger tasks lists may make this more difficult than using cut and paste as a simpler method.
Use cut to get the task into your clipboard.
Navigate to the summary task within which you would like to move the task. You must click within the summary task view to paste it.
The second point above is very important or moving the task will not complete. If you try to paste into the summary task by clicking the summary in the list it will not work. You must be in the view of the summary. In this example, we are moving Joe's task into the summary task named Engineering by first clicking int the detail view of the Engineering summary task.