By jailbreaking your Apple TV 3, you can modify your device and install unique themes through third-party apps from outside of Apple's built-in App Store. For now, Apple TV 3 can only be jailbroken using a software called Snow3rd on Windows computers.
Step
Step 1. Make sure your Apple TV 3 is running iOS 5.0.2 or earlier
Snow3rd cannot jailbreak Apple TV running iOS version above 5.0.2.
Go to “Settings” > “General” > “About” menu to find out which iOS version is installed on your Apple TV 3
Step 2. Make sure you can access or use a computer running Windows 7, Windows Vista, or Windows XP operating system
Snow3rd is only compatible with those older versions of Windows, and is not compatible with Windows 8 or Mac OS X.
Step 3. Visit the Snow3rd website at https://snow3rd.com/ and click the “Snow3rd Download” link
Step 4. Select the option to save the.zip file to the computer desktop
Step 5. Close all applications and end all running processes on Windows computer
Step 6. Connect Apple TV 3 to the computer using a micro USB cable
The Apple TV USB port is on the back of the device.
Step 7. Disconnect the Apple TV from the power source/wall socket
The only active wired connection on the Apple TV 3 is the micro USB cable connection.
Step 8. Open your computer desktop and double-click the Snow3rd.zip file
The contents of the file will be extracted and a Snow3rd dialog window will appear on the screen.
Step 9. Click the “Jailbreak” button
The jailbreak process will start and the progress will be displayed in the status bar. This procedure takes a few minutes to complete.
Step 10. Close the Snow3rd dialog box after the message “Jailbreak Successful” is displayed on the screen
Step 11. Disconnect the Apple TV 3 from the mini USB cable, and restart the device
Step 12. Reconnect Apple TV 3 to the computer after restarting, then open iTunes on the computer
Step 13. Make sure iTunes recognizes the Apple TV 3
If iTunes recognizes the device and displays the Apple TV icon in the upper-left corner of the window, the jailbreak has been completed successfully.
Step 14. Connect Apple TV 3 to a power source and HDMI cable
Your Apple TV 3 is now jailbroken so you can install and run jailbroken apps downloaded from outside the App Store (via the web).