There are four files. One has the Car with new spoiler, taillights and rims. The other has two Cars with different spoilers, taillights and rims. These two files also have duplicates where no materials have been applied on the car, so you can easily use your favourite rendering engine and apply fresh materials on the car. Each part of the car is named properly. Large groups have been made and the layer editor has proper layering, so that it is easy to find objects.
Also, objects belonging to a group (e.g. engine) have been grouped. Simply ungroup them (GROUP>UNGROUP) so that you are able to select individual objects. It is not recommended that you ungroup everything however...