Hi Murthy,
Did you download the parts from
www.ptc.com/go/firstkop? Or did you download it form the
www.firstcadlibrary.com?
If you downloaded it from the firstcadlibrary.com, the files are not native Pro/E. You would not be able to modify the dimensions.
I suggest you grab the same model from the ptc.com site....as they are native Pro/E models.
let me know which ones you grabbed and we can discuss the steps to edit.
mark