You will spend a lot of time and money and get some 10hp more at best. It is hardly noticeable. You could also change sprockets - that is a bit more noticeable I think, but the best thing to do is just get another bike. It will be cheaper and simpler.
Things to consider adding more power (and riding it for all it's worth!) are suspension and frame stiffness - both not up to the task of high speed riding on FZS. They are OK. Especially for a 95 hp engine, but for over 100 hp high speed - I'd just get a Thundercat, R6 or something like that. CBR600F or RR should be fine as well.
However, if you have enough time, money and like fiddling with a bike that works, KN air filter, DynoJet kit, Arrow/Scorpion/Akrapovic end can (or full exhaust tubes as well) will give you more hp.
To tame it all and stay on the pavement, you will also need some better, stiffer, suspension. Wilbers monoshock and fork springs.
That should make a nice tuned Fazer.
Correct me if I got prices wrong:
KN filter around 70 euros
DynoJet kit 100 e
Arrow end can 350 e
Decent Wilbers mono shock 500 e
Wilbers springs - no idea.
That's around 1000 euros. If you have money and time, you will be happy. Forget price soon and remember the ride forewer. However, if you want quicker sportier bike, selling FZS and getting another motorcycle is the best thing to do.