NO Manual?....anyways....put the bike on a stand (wheels off ground). Measure from the axle to a set point on the fender, or seat bolt. Record measurement. Now take bike off stand (you'll need a second person for this part) and sit on seat, with feet on pegs in a normal riding position. Measure from the same two points again.
The difference between the two measures is your sag (or race sag). It should be somewhere in the area of 100mm. If it is less, you will have to lessen the preload on the spring, more than 100mm, you will add preload to the spring.
To cahnge preload, you will notice two collors on the top of you shock spring. The top collar is a lockig collar. Use a punch and loosen the top one off. Now you should be able to grab the spring and turn it, along with the bottom collar (one next to the spring) to add or reduce preload on the spring.
Measure sag again and adjust until you have 100mm, or there about. You can now tighten the lock collar back down.
Now, take the bike off the stand and take the same measurement with bike just under it's own weight (not with yo on it). This measurement should be in the area of15-25mm. If it sags less, you may need a heavier spring, if it sags more, you may need a lighter spring.