FireCore claims that Seas0nPass is an open-source, easy-to-use method of adding IPSW files to the Apple TV, so it can also be of use if you've already jailbroken your AppleTV. However, you will need a micro USB handy you'll have to tether your Apple TV to a computer in order to perform the hack.
Need to undo the jailbreak? Seas0nPass will let you restore your AppleTV to factory settings via iTunes--making it as though the hack never was. Sneaky. But don't attempt to install Seas0nPass on any other Apple device, as it won't work.
Keep in mind that Seas0nPass is still very new and may have a few bugs that need straightening out, so as will all hacks, proceed at your own risk.
As feedback on the suggests, although many users are content with the software's results, a lot of people are having problems when they reconnect the Apple TV to their sets (Did we mention it was brand new?). Hopefully, FireCore will get round to answering the questions and fixing the problem shortly.
If you know what you're doing and want to give it a try, check out FireCore's for the full instructions and download.