I believe your compression adjustment is at the bottom of your forks. It's a little straight slotted screw. Clockwise rotation of the screw makes compression harder, or stiffer. Counter-clockwise makes the compression softer. Increasing the preload on the fork springs requires adding spacers to the inside of your fork, not recommended unless you are comfortable with taking apart your forks. It sounds to me like you are kind of big and heavy and the stock springs on your 250 are not suited to your size. Search around in these forums, and on the internet in general for "race sag." By setting your race sag, you can determine if you need stiffer or softer springs in the front and rear. In any event, when making adjustments to your suspension, make one change at a time and test it while riding in a particular area. This way you can feel what is changing and whether it is for the better or worse. Good luck.