If you’ve already installed iOS 6 GM on your developer-registered iDevice, the good news is that it’s possible to jailbreak said iPhone, iPad or iPod touch under the “Gold Master” edition of iOS 6.
All you need to do is download redsn0w 0.9.13dev4, and plug your iDevice into the computer. Then, in redsn0w, click “Extras” and “Select ISPW.” From here, you can select any iOS 6 .ispw file (apart from iOS 6 beta 4), and then begin the jailbreak process. After a short while, your iOS 6 GM-powered iDevice should be jailbroken. Just remember, this is a tethered solution, meaning you’ll need to boot-tethered if your iDevice powers down unexpectedly, and that this jailbreak solution supports Apple A4-powered iDevices only.
Head on over to the iPhone Dev-Team’s website for instructions, download links and more. Good luck!
Source: iPhone Dev-Team