You don't use the code to redeem again. Just go under the Purchased tab in the App Store app and re-download it. You'll have to re-download if you already installed it because the installer deletes itself after installation.
For future reference, you can avoid the auto-deletion simply by cancelling the installation the first time, and moving the installer from inside the Applications folder to the Desktop (or whichever folder you want to keep it in), then open the installer from the new location. (It will only auto-delete if the installer is run from inside the Applications folder.)