Sorry, I was being quite brief. If you select the drive on the desktop by clicking on it once, you can then "Get info" about the drive from the finder "File" menu at the menu bar at the top of the screen. That will open the Info window for your hard drive, from there you will see the same image for your drive in the upper left hand corner of it's "Get info" window, you can pretty much drag and drop another image to that little image window to change the drives icon image.
I hope that is more helpful.