Even if you could replace the CPU, none of the processors supported by that laptop would be game-ready, nor is the cooling system capable of handling such a processor. I also suspect the motherboard (and power systems) of a $300 laptop would be stressed to failure by anything larger than what it already shipped with.
Like iceblitzed said, save up your money for a new laptop, and purchase a model that can do what you want straight out of the box. We can help you if you don't know where to start looking.