Here are the instruction on performing untethered jailbreak on your Apple TV 2nd generation.
Step by Step Tutorial To Jailbreak Apple TV 2G Using Seas0nPass:
Step 1: Download the latest version of SeasonPass from here.
Step 2: Double click to extract the archive you downloaded. Then double click the extract application to launch it.
Step 3: You will be asked to sign in as an Administrator. Enter your username and password then click the OK button.
Step 4: You will be asked to enable UI Scripting. Click the Enable button.
Step 6: Seas0nPass will now download the latest Apple TV firmware file.
Step 8: Once your custom IPSW file has been created, Seas0nPass will ask you to connect the Apple TV to your computer via a micro-USB cable and use the remote to put it into DFU mode by holding MENU and PLAY/PAUSE for 7 seconds. The power cable should be unplugged during this process. Tip: Press the buttons and insert the usb cable at the exact same time.
Step 9: Once your Apple TV has been detected in DFU mode, Seas0nPass will upload some files, automatically launch iTunes, and beginning restoring to the new firmware.
Step 10: That’s it! Your Apple TV is jailbroken!