Method 1. In the Origin client.
Log into Origin with the EA Account you want to add your game to.
Click on the Origin menu at the top left.
Select “Redeem Product Code”.
Enter the serial key on the back of your game manual.
The game will be added to your "My Games" section of Origin.
Once the download is complete, you are ready to play.
Method 1. On the Origin website.
Go to www.origin.com/account
Log into your Origin account using your Origin email address and password.
Select "Redeem Product Code" from the left menu.
Enter your product code on the Redeem Your Code page.
In the second case, you still have to wait until your game is downloaded and available in the Origin client.