How can I safely overclock my MSI N240 gt 512mb ddr5

Hi,
I just upgraded my PC with a new video card, MSI N240 gt 512mb DDR5. Some of the games work flawlessly, but the others still freeze. I've read that games like GTA 4 and Fable 3 needs a better GPU. The thing is that my Video card is capable of over clocking but I am a bit worried about the risk if ever something went wrong. Can anyone help me over clock my GPU safely? Thanks
