[Problem]Nvidia GT540M Optimus

Hi! elitepvpers

I have acer aspire 4750G

This is my lapotp spec


Procecor: Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz (4 CPUs), ~2.3GHz
Memory: 6144MB RAM
OS :Windows 7 ultimate
vga: nvidia gt540 and Intel hd graphics family

I have problem with this laptop vga

i test play need for speed hot pursuite,Blur,Cod mw3, Battlefield mw3

And i get verry low fps on need for speed hot pursuite,blur and battlefield 3
why this happen?
i already setting use nvidia gt540 to play this game but still have low fps?
someone can help me?

Which resolution do u use?
And you know, that youre graphic card aint the best?