All existing owners of The Witcher 2 received free upgrades to the Enhanced Edition, and could pre-load the update starting 11 April 2012. All new copies on PC and Xbox 360 shipped with the additional content on board. The Witcher 2: Assassins of Kings – Enhanced Edition added over 10GB of new content, including four hours of gameplay, arena mode, new tutorial, 36 minutes of cinematics including a new intro created by Platige Image and an outro, as well as a host of fixes to gameplay and the interface.Go to: http://store.steampowered.com/ and download STEAM client
Click “Install Steam” (from the upper right corner)
Install and start application, login with your Account name and Password (create one if you don’t have).
Please follow these instructions to activate a new retail purchase on Steam:
Launch Steam and log into your Steam account.
Click the Games Menu.
Choose Activate a Product on Steam…
Follow the onscreen instructions to complete the process.
After successful code verification go to the “MY GAMES” tab and start downloading.