Instructions
Download the desired add on content from the PlayStation Store. You can access the PlayStation Store from the main PlayStation menu when you first turn on the system. You will need to have an active Internet connection and PlayStation Network account. Most downloadable content will have a price attached, so you will need to purchase credits before you download it.
Start "Dead Space" like normal after the download is finished; this should only take a few minutes, depending on your network speed. The content will be automatically detected and loaded upon starting the game.
Start a new game or load a previous one.
Locate and access any of the in-game stores. The stores are scattered throughout the USG Ishimura and are typically easy to find. They are large consoles located in wall alcoves, over which the word "store" is displayed in large yellow letters.
Purchase the downloaded content from the store menu in the same way you would purchase any other equipment in the game. The downloaded items will be listed as costing zero in-game credits. New armor that you purchase will be instantly equipped after a short cut scene. Purchased weapons will be moved to the inventory, allowing you to equip them immediately or stash them at the store like other inventory items.