I have been riding my Ninja 250R on factory default preload position 1 and I find the bike was very squishy and hard to do cornerings. The manual say position 1 is for average build rider of 68kg. I'm 6'1" tall and weighs 89kg, so the standard position is not too suitable me.

After a few minutes of search on the net and reading the manual, I decided to change the preload to position 3. I found a way to adjust the preload without removing the chain guide as manual suggested and the bike on its side stand.

Firstly, I unpacked the tool kit (which is located under the pillion seat) and took out the special wrench.
Secondly, got the wrench around from above the rare wheel instead of removing the chain guide. I don't know how it will be if the bike was lower by a couple of inches but with the standard height it was quite easy to fit your arm around the back to reach the preload adjuster.
Thirdly, I position the wrench in the groove, make sure the wrench is perpendicular with the preload adjuster. Then, turn the wrench counter-clockwise to set it to position 2 etc. Make sure it click on to the next position after you turn the adjuster. If the adjustment is a bit hard to turn just use a bit of force.

I find the position 3 is best setting for me and after a test ride around the block the bike is alot more responsive and easier for cornering at higher speed. Try which position suits you best by trying position 2 and so on. I wouldn't go more than position 4. It'll become pretty harsh and stiff to ride and you'll feel every bumps on the road which won't be great for your back and riding could become very uncomfortable. Anyways, I can put up some picture if you guys need.