asus a52jc video adapter switching

hi

i have this type :

CPU : i5 core

GPU: nvidia 310M 1GB

i bought it specifically for the exteranl GPU (nvidia's)
but when i turned it on i noticed it uses intel graphic buillt on the CPU (as i understand, and didnt know it had one)

i did some research and i only found it could be this new called "NVIDIA's Optimus" technology of Nvidia tested the first the time on the Asus notebooks, similar to the SLI for saving battery.

its all good but how do i switch between the two graphic's ( if i can)

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