Instructions
Turn on your PS3 console and scroll over to the "PlayStation Network" icon located on the far right-hand side of the menu.
Scroll down to the "PlayStation Store" icon, which looks like a shopping bag, and press "X" on the PS3 controller to select.
Sign in to your PlayStation Network account using your ID (E-mail Address) and password. Press the "Sign In' button to access the PlayStation Store.
Navigate to the top-left corner of the screen and select the "View Downloads" icon. A list of game downloads will appear.
Scroll over the game you want to re-download and press the "X" button on your PS3 controller, which will initiate and complete the download. You can track the download by following the progress bar. Once the download is complete, the progress bar will disappear.
Check to see if the re-download process was successful by exiting the PlayStation Store and clicking on the "Game" icon in the PS3 main menu. Scroll down until you find the game you had just finished re-downloading.