You must first register your Licence key on the forum here. If you click on "Profile" in the centre of the yellow bar at the top of the screen you will find that there is a space to enter it if you scroll down a bit. One you have done that you should see the word "EXTREMES" below your name on screen. If you have the Steam version of the game you will also have to enter the Steam licence key as well.
I hope this helps.
Regards,
Traddles
