Tune up my Spring air soft pistol questions....?

I have a Pietro Beretta mod. 92fs-cal 9 Parabellum spring power air soft pistol that used to work very well. Now, though, not so much. After having friends and family dry-fire the thing upwards of 80 to 100 times its not as powerful as it used to be. I think its because the springs are messed up now, but i don't really know to much about sir-soft guns internal workings. I want to know where i can find a tune-up kit that will make it shoot stronger and act a little more like new. And if you know any videos that give a little tutorial on how to upgrade/tune up the pistol feel free to post that to. Thanks in advance