Need help with Dynamic shadows

[Nikkokonut]

Hi, I love Left 4 Dead 2, and other games like Dead Space 3 and all that because this kind of games have a great dark atmosphere were lighting and shadow effects are really what shines in this kind of games, but I don't have Dynamic Shadows for Left 4 dead 2 and Dead Space 3, I was wondering how you can turn this on, by the way my laptop is LG N550 and It has two graphics cards, I'm using the Intel i5 graphics card right now and I don't know how to switch to the radeon, the Catalyst Control center is not giving much needed informatioon on how to switch graphics cards.

I'm not really that smart when it comes to graphics and all that, but I need help on this matter, thanks in advance.