You may not want to try a spring swap by yourself if you're new to AEG's. Its doable but will require a lot of time and patience. I'd suggest you find a gun-doc on the forums here who can do it for you.
You won't be able to attend most games with a gun shooting over 430fps. Outdoor games are usually around 400, indoor ones are 350. There are exceptions but such games are rare.
Also keep in mind that the 400/350 fps is just an upper limit. High fps does not make an accurate gun. Lots of Tokyo Marui guns shoot ~280fps but are still ridiculously accurate. You probably won't notice a drop in accuracy by going from 430 to 390 fps. You will however notice an increase by adding things like a good hopup (the piece that provides the backspin on a BB...for longer flight) and tightbore barrel. As you use your gun (and inevitably break stuff due to natural wear), be sure to upgrade to quality parts.
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)