GPU switching? Lenovo Z510?

I have bought the Lenovo Z510 59-405838 and was trying to play GTA4. But whenever I start the game it never comes on as full screen. And in the settings of the game it shows that my resource is only 27mb. So I think it is using the intel hd graphics instead of Nvidia. The laptop is on high performance profile and I even tried running the app with high performance graphics by right clicking. But no luck.