1. Download the Gran Turismo 5 Code Generator
2. You will need to complete a survey to verify that you are a human and not a bot, this is to protect the number of file downloads. Simply click one of the free offers, complete a survey and the button will turn green.
3. Save the file to your desktop and open it.
4. Click the generate button and wait for a code. When you are presented with your code, write it down on a piece of paper as you will need this code.
5. When you have your code saved, redeem it on the Playstation Store website.