power steering fluid....

(I did the searches, I need more information)
Steering to the right is harder then steering to the left.
I checked my power steering fluid level....and it was just a little bit over the MIN line.
Is this okay? Should the level exactly be in the middle between MIN and MAX?
If I need more ps fluid the manual says that you cannot just add it....so then what else has to be done? flush it totally then add it??

thanks,
eddie.
p.s. i thought that if u had ps fluid problems, then steering would be harder both ways?