you don't cause I think you only get about 1/4" of range with the coil and based on how fragile the K4600 ones are it's not worth mucking with. you need to change the width cap to a different value.
read this page:
http://www.thegleek.com/bobroberts/width.html
do a Find to the part that says "Wells-Gardner K4600 Series - C615", below is a list of the different cap values. lower capacitance = wider picture, higher capacitance = narrower picture. find your C615 and take a picture of the numbers on it and post it in this thread. APAR sells a kind of universal width cap kit of various values.
I've personally only ever changed width caps on K7000s and K7203s in the past. I have a K4900 in a Dig Dug at work that I really need to change.