Instructions
Turn on your PS3 and scroll to the "Network" tab.
Highlight the "PlayStation Store" icon and press "X." If you are prompted, log into your PlayStation Network account. If you do not have a PSN account, you will be brought to the screen where you can create one.
Select "Add-Ons" from the menu tab in the PlayStation Store, and highlight the icon from "Disc-Based Game Add-Ons" Press "X."
Select either the "A-L" or "M-Z/#" title icon and search for the game you wish to download content for.
Select the game you wish to download content for and browse the downloadable content available for that game.
Select the add-on content that you want to download and select "Purchase." The content will be downloaded and installed to your PS3.