For SilicaCAD 2013 and newer versions: 
Uninstall SilicaCAD ® from the old PC through Control Panel or SilicaCAD Centre. Proceed to the new PC and register the program using the same serial number. 
For earlier versions of SilicaCAD: 
Uninstall SilicaCAD ® from the PC so far used going to the menu: 
Start> Programs> SilicaCAD 200X pro ENG> Uninstall SilicaCAD Pro 200X 
Proceed to the new PC and register the program using the same serial number.