Batman Arkham City

Arkham City is not a well threaded game. The game was not well ported, so you have this sort of stuff happen, it will lean very heavily on one core, and not do much with the rest of the CPU. There isn't anything you can really do to change that.

Really though, most of your performance problems are probably related to your graphics card. The 7450m is not a strong graphics card, probably only somewhat better than Intel's integrated graphics. The only way you are likely to boost performance is to turn down your graphics settings. Arkham City can be a graphically demanding game, especially if you try to play it in DirectX 11 mode.