Instructions
Turn on your PS3. Select the "PlayStation Store" option in your PS3 main menu.
Select the "Themes and Avatars" option in your PlayStation Store main menu.
Select the "PS3 Themes" option in the themes and avatars menu, and then select the "P-S" option in the next menu.
Select the "PixelJunk: Monsters" option in the next menu, and then select the theme you would like to download. Since all of these themes are free, the download begins instantly. After the download, the monster theme will be available on your PS3.