I would just get a different graphics card. Your current card is extremely weak and probably not worth the effort of overclocking just to get a couple FPS extra. There are plenty of graphics cards <$200 that pack plenty of performance if you don't want to spend too much on a new card.
Still being a highschool student, even cheap graphics cards are out of the question So overclocking my current one is the only solution in sight. How much fps improvement will there be aprox. though?
Hey, I'm in highschool too and look at the rig I have in my sig. (no I'm not a spoiled rich kid, I have a summer job) Honestly I would do whatever you can to scrape together $100 for a better card if you can, the difference will be enormous. If you can't do even that you can download a tool like MSI Afterburner or EVGA Precision and overclock your current card. Depending on how much of an overclock you do I'd estimate a 5-10% gain at most.