Hard step would be putting the shaft of a more lofted iron into a less lofted head (i.e., 9 iron shaft into a 7 iron head).  Soft stepping is putting the shaft of a less lofted iron into a more lofted head (7 iron shaft into a 9 iron head).  Titleist irons use taper tip shafts.  Hard stepping stiffens it slightly and soft stepping gives a little more shaft flex.