rear sprocket size

i need a new rear sprocket on my kz900. it currently has the factory one on it. what i want to do is drop the rpm's at cruising speed in 5th. i think its got 35 teeth on it. what would i need to do to drop the rpm's? go higher on the tooth count or lower? i searched around and found some info on a kz650 but i doubt the tooth numbers would be the same. thanks for the help.

If you want to drop the rpm.s put a smaller sprocket on the rear or a bigger one on the front. If your rear sprocket is worn it's a good idea to also change the chain and front spocket also. I know it's expensive but if you put only one sprocket on the old streched chain will wear it out sooner.
As far as changing the ratio, I feel it's better the increase the front sprocket 1 tooth, the sprocket is bigger, it won't wear the chain as fast.
On my 650 adding one tooth to the front dropped the rpm by 400 rpm. My next chain I am going to decrease the rear sprocket by 2 teeth and get the same size front I have now, which basically will drop the rpm by another 400 rpm. I'm more into enjoying long rides than performance.
Ride safe