How can I overclock my laptop safely?

I have a dell xps 17 and with a i7 2720qm cpu and a nvidia geforce gt 555m graphics card. any way does anyone have any tips onn how to overclock my gpu safely as possilbe and what are the best programs for doing it well and safely. I am doing this because i want to play battlefield 3 as best I can, and as a side question I have heard their are some programs that make you game priority and defrag it and stuff like that does anyone know what this program is called and if it works?