Hello I'm new to Ubuntu and all in Linux. I have a computer with 8 GB of RAM and a processor Intel core i7 3770S and video card nVidia GeForce 640M and and Intel integrated graphics. In my system information is displayed only integrated graphics Intel. How do I switch to the nVidia GeForce 640M (in the BIOS do not have this function)? Sorry for the grammatical errors, I do not know much English.