Whats the best way to jailbreak my Ipod?

I have my ipod 2g jailbroken on firmware 3.1.3 and i would like to upgrade to a jailbroken 4.0 software. In Redsnow 0.9.5 i see an option that says already pwned, what doest this mean? what is the best way to go about upgrading and jailbreaking? PLEASE HELP thank you =)