Hello, i just It is supposed to have Nvidia Geforce GT 540M graphics card in it, but it seems, that it's using integrated one instead (i have intel i3 core).
Is there a way to switch between these two cards and how?
yes, this is called nVidia optimus technology (ability to switch between integrated and dedicated GPUs), you should be able to configure it from control panel or nVidia Control panel (your graphics card properties section)
I'd recommend you google Optimus tutorial or something like that to help you figure out how to set it up the way you want it to work
Also, I'm not sure about your particular laptop, but some models have an external button that turns dedicated GPU on/off
Look through your manual to find out how to switch between the nVidia GT 540 and the Intel HD 3000 graphic core. You should at least be able to do via software. There should be an Optimus / nVidia icon in the icon tray on the right side of the task bar.
Your laptop may have also have a physical switch to turn on/off the GT 540 as stated above. My Lenovo IdeaPad Y470 has such a switch. For the few games that I've played on my Y470 (Crysis, Fallout 3, Civilization 4, Mass Effects) it always defaulted to the nVidia GT 550m unless I manually switched it off.