as a consumer you can't - it is copyright software and costs a lot.
as a garage you can get it under licence from Audi.
having said that, you can pick up hooky copies on ebay, but I'm sure audi-sport.net does not condone the sale/purchase of hooky software.
the difference is not the size of the bonnet, it is the raised area up the middle, which is more pronounced on the later cars, to follow the lines of the grill up to the windscreen. assume we are talking about the 3 door, and not the 5 door??