2 graphic cards - how to switch to best one?

Hi,

Sorry for 2nd thread so quickly...

I have two graphic cards, device manager says I have:

ATI Radeon HD 3200 Graphics
ATI Radeon HD 3400 Series

So which one is my computer using? If the 3400 is better can I switch to that one? btw both are working fine according to device manager, there's no problems I just am curious if I can switch to the better one.

Thanks,
Karl