Instructions
Ensure that your console has an HDMI port. Check the AV port area on the back of your console. If your console has an HDMI port then it will be located next to the component/composite port. When the Xbox 360 was first released, only the "Elite" package included an HDMI port. Microsoft then gradually started manufacturing every console with an HDMI port in 2007.
Purchase an HDMI cable if necessary. You can buy any brand of HDMI cable and it will be compatible with the console.
Power down the console and connect one end of the HDMI cable to the console's HDMI port. It does not matter which end of the HDMI cable you use.
Connect the other end of the HDMI cable to your television's HDMI input.
Turn on your console and access "System Settings" by pressing the Guide button on the controller, scrolling to the "Settings" tab and choosing "System Settings."
Choose "Console Settings" then "Display." This will take you to a menu where you can modify your HDTV settings.
Choose "HDTV Settings," then select your TV's maximum resolution.