How to change an existing "Game Object"?

Question

I’m starting now with Unity3d and for that I took the example that comes with the package, the car.unity.

I read a lot of documentation, but I couldn’t do something very simple...

1. How to change the shape of an existing one? I’m not talking about color or texture or even position, but the very way!
2. There is no "internal" Unity tool to do this?
3. SOMETHING ELSE: I tried to "export" this "clue", to be able to edit by an external tool (like Blender) but I was frustrated again, I couldn’t even do that.

To be more direct, I would like to simply change the route of the track put more curves, straighter, things like that! And since you already have a clue there, I would like to "update" the one that already exists!

Thank you!