it's a matter of double clicking on a vertice, and changing it's x, y & z values. it's a very time consuming and frustrating process- just like most things to do with GP3!!!
just play around with things, you'll figure out the best process to use for yourself, and it'll probably take you a few goes to master it!
i've figured out how to make carshapes and what not, but am struggling to figure out how to alter helmet positions and the like- does anyone know? everytime i change the helmet position it never saves