Instructions
Log in to your PS3 user account on the PS3 main menu screen, and scroll over to "PlayStation Network."
Click on "PlayStation Store" and log in to your PlayStation Network account. If you do not already have one, you must go to the PlayStation main webpage and sign up for a new account with your email address and a chosen username and password.
Click "Yes" if you are prompted by a message saying that a system update is required. The PS3 must be fully updated before you can access the PlayStation Store.
Select the "Add-ons" menu from the left screen on the PlayStation Store menu. This lets you search the online catalog for game extras and downloadable content.
Choose "Disc-based" add-ons from the menu screen.
Navigate to the option listed "A-L" to scroll through add-ons for all games starting with those letters. Scroll down the list until you see "Guitar Hero: World Tour" and select the game.
Look through the list of downloadable songs for your game and highlight the one you want.
Click "Download" and agree to purchase the song. Once purchased, the song will be downloaded to your PS3 hard drive and will be accessible when you restart the "Guitar Hero: World Tour" game.