If you add a new shape to the top of a chart, the shapes will be off-center. To move them to the center, group them, then drag them.
(Note: After you group shapes, some features aren't available on the Org Chart toolbar. For instance, you can't insert shapes to grouped shapes using Insert Shape.)
A note about styles
If you move a shape in a chart that has already been hand styled, and you want the moved shape to assume the styles of the shape it's now next to, use the Format Painter button to duplicate the styles from one shape in another.
You'll do this in the practice session.