|You can't change the graphics. The only way to upgrade would be to buy a completely new laptop with better graphics. Gaming laptops are not cheap. Figure at least $1000.|
"what sort of games i can use"
Did you check the link I posted in response #1 ? Here's one statement from that article: "Only less demanding 3D games and very old games may run fluently in low detail settings. Sims 3 and F.E.A.R. for example achieved 30 fps (with stutters) in low deatails and low resolustions".
Have a look at the following chart - it will take a while to load. Scroll down about 3/4 of the way & find the 4500M. Anything in green is playable.
Or if you have a specific game in mind, you can check playability with this:
Can You Run It?