KDX rear shock improvements

Hi, I have just bought a KDX 200. It is quite a neat specimen, but the rear shock is a bit soft.
Is there a simple remedy for this? Will dialing up the pre load make a difference?
Otherwise are there stronger springs available for these bikes?

I am in the jhb area, is there anyone around who can do this sort of stuff? At the same time I guess I should also look at giving the shock a basic service while it is out.

Any suggestions will be appreciated.

Thanks
John