First I'm going to echo everyone else and tell you to go get age verified, it's painless and well worth it. http://www.airsoftcanada.com/showthread.php?t=74996
Now to answer your question, yes you can change FPS rather easily it's just a matter of changing a spring inside the gearbox, a $15 part.
Going up in FPS can sometimes require a stronger motor to accommodate the stronger spring but going down in FPS is usually no problem.
A gun doc can do this for you if you are not comfortable doing it. See this thread to find one in your area http://www.airsoftcanada.com/showthread.php?t=72809