To move a hanger to a new location on a duct, go to
Ribbon: DM HVAC->3D-BIM-> 
Move Hanger
Pulldown Menu: DM HVAC->3D-BIM->Move Hanger
You will be prompted to identify which hanger is to be moved.
Select hanger on duct to move:
You will then be prompted to identify where the hanger is to be placed.
Select the new location
The hanger will be moved to the new location. The location of other hangers will be adjusted based upon the new location of the hanger.