Need help with my computer and overclocking?

Hi, I just found out about overclocking and watched a few videos on how to do it but not sure if my computer can handle it. I'm thinking of putting it to 4Ghz but if I cannot please tell me what I should clock it to. My computer is: CPU: i7 920 cooler master seidon 120xl with 2x Corsair Sp120 Performance edition GPU: ASUS gtx 660 MOBO: Asus p6t deluxe RAM: 4x 2GB sticks PSU: 775w HDD: WD 1x 1TB OS: W 7 Ultimate And 2 more 120mm fans in my case. Thanks.