Discrete Graphics Question?

I got the 5.1 and it has discrete graphics. Do I have to turn that on, and if I do how?

Thanks,

Open System Preferences and goto Energy Saver.

At the top you should see an option for Graphics:
Better battery life = 9400M
Higher performance = 9600M GT

Select the one you wish to use, you will then need to log out and back in again for the Mac to switch graphic cards.

Thanks

Thanks man. I need that for the Sims 3.