adjust wheel?

I have a scott tiller and its 7 years old and is gear driven the front wheels have an adjustment knob where I can pull the knob out and roll the tiller without starting it and I notice that now when using the tiller that the adjustment pushes out while tilling and the tire stops pulling as it should it has a nut, butterfly adjustment which screws in and out and the spring and washer on a bolt with a hex head if I could get at the hex head I believe I could tighten that but cannot figure out how to get at the head of the bolt it is inside the shaft. Any help would be appreciated.