No no no, don't f*** about with it unless you know what you're doing
It sounds like you're talking about the pre load adjustment on the top of the spring. Adjusting that gives you 'pre-load'. ie how far down the rear sits, it needs to be set static, ie with no weight, with the bike upright measure from the axle virtically to a fixed point on the seat unit, then lift the rear until the shock 'tops out' ie fully extended, and re measure, the difference between the two is the pre load measurement. On a race bike it should be anything from approximately 5 to 12mm. I don't know what it should be on a standard bike with standard shock. Do not adjust it to just raise the ride height, you'll lose pre load resulting in the shock topping out all the time.
Having said that you may be talking about the top shock mount. You can raise the rear ride height by lowering the U shaped bracket that the top of the shock mounts too. Raising the rear will make the bike turn faster.