This is what it says on the playstation blog in today's release's post :

Step 2: Redeem Your Promotion Code
Please note: if you’ve participated in the second PS4 beta, this step is optional, as you already have the game client installed on your system and only need to update it. You still need to go through step 1, though!
Boot up your PS4, log in to your PlayStation account, and go to PlayStation Store. Make absolutely sure that you have the correct PlayStation profile active before you enter the store! Promotion Codes can only be used a single time, so using it on the wrong account would leave you stranded.
Select “Redeem Codes” from the option menu displayed at the bottom left of the screen and enter the promotion code.
When you’ve done so and confirmed the regulations, you can start the download.
If something goes wrong with the download, you can try to restart it using the “Library” option in the PlayStation Store menu.