When a heads up display dimension is selected, a small dialog appears. Inside the dialog is a text box displaying the dimension value. A new value is entered in the text box, and when accepted, the component is updated and the heads up display is dismissed.

If you need to review or modify the whole set of DataGroup properties associated with the selected component during the modification of a component dimension arises, then check the check box next to the dimension. This opens the properties/parameters panel in the Modify Component (the transient UI of Placement) dialog, filled with the selected component DataGroup properties.