Need to upgrade gpu in all in one pc...?

-i have a lenovo thinkcentre all in one. i've searched online but all i've found is that the embedded graphics card can be disabled and another graphics card can be added. i want to upgrade the amd mobility radeon to an nvidia 580m because im sick of playing games on 1024*768 on low settings. i cant buy a new pc anytime soon....is it possible to try the embedded graphics card disabling technique?Yup the 580M will probably be great...but ...were do you plug it in??? The best I can gather, the 580m fits in a special notebook size PCIe 2.0 slot...the lenovo doesn't have???