Yes, I think Saan Dai is correct. You dont need to reply eventhough your I-20 has changed. you may be worried that the new I-20 doesn't have the stamp as the previous one. It doesnt' matter. But you need to meet your international advisor. My university gave me another I-20 once I arrived here and again another one after some day..( I have 3 I-20s). Now I dont need the older one.