You could start by reading the guide fully.
What is the problem you are having?
You have DLed the porshe right?
Have you DLed the tool thing? And replaced the files it tell you to in the note pad?
If you have recently bought the game it wont work cause its the "newer" version of the game. And im not sure on if there is a patch out that could fix that or what, but im assuming there would be.