Instructions
Press the "A" button on "Explore New Games" from the "Game Marketplace" tab on the Xbox 360 Dashboard.
Press the "A" button on the "Y" panel from the "Titles A-Z" tab.
Scroll down and press the "A" button on "Yu-Gi-Oh! 5Ds."
Press the "A" button on "Free Trial." A confirmation window will appear.
Press the "A" button to confirm the download of the game's demo.