Originally Posted by JuSt BLaZe
You have to choose it from the main menu. It's a seperate game. Which means, you start without your so far collected cash, cars & clothes from the main game!
Thanks for the answer!
I figured out my problem yesterday, just forgot to come back here. It`s a glitch in the game. I bough it back home and was going to play during the weekend at my girlfriend`s house where I have another X-Box.
Turns out there`s a glitch and the DLC will only work in the console that you used to buy it. I will have to wait until monday night to play it