Press the Control Key on your keyboard and then on the piano roll at left of midi window click the note you want (e.g closed hit-hat). Every instance of that note pitch is selected and highlighted in orange. You can then move it to different hi-hat sounds as you wish - in this instance to see how a 1/4 shank might sound instead. below is pic of the snare being selected.
It also allows you to amend the velocities etc of just that single instrument sound. It's one of the best features of S1 midi editing.
Just be cautious if you work your drum midi track in sections. this method will only work on the current selection, so if you want to change teh note for the whole track then ensure you merge all the sections in the drum track (highlight them and click G)