Bhuvaneswaran if you mean scaling from 'stretching', then there is a provision for scaling in HFSS. Select your design, right click on it. Then go to Edit--->Scale. Its quite simple. Good Luck!!!
Yes, If you want to scale its parameters then go to edit for that particular part and change it, but resonant frequency can't be changed directly. If you have reason like changing the design frequency or change in your parameters, then you can think. Give me some more detailed of your work, so that i could help you.