If your bike is like mine (2007), there are air valves on top. These are to let air that has built up out, not to put air in. Make sure to release any pressure in there. Other than that, Paper is right that the only changes you can make is to the springs, oil viscosity, or the preload spacer. If you want the front to be softer, you could remove the top caps and the spacer is right there on top. It is 5 1/2" . You can cut a piece of 3/4" PVC to be 5" long and put that in place. This will loosen the tension on the spring. If you want it stiffer, cut the pipe 6 or 6 1/2 inches. Of course do this to both forks.
2009 KLR 650