Q: How do I switch a drawing I created using one scale to a different scale?
A: Use the DIMSCALE system variable to set the scale of the drawing. Make sure it is set properly.
Run the DM->Utilities->Coordinate Drawings and Database command. This command will update all the devices, text, and symbols inserted by Design Master on your drawing to the current scale.
For HVAC, you will also have to redraw the ductwork using the DM HVAC->2D Drafting->Draw Double Line command to update the size of the ductwork labels.
Text and symbols inserted using standard AutoCAD and not Design Master will need to be updated manually to the new scale.