Generally, to edit cockpit shape you need CarEditor.
1.You click "import car from exe"
2.Go to the left and you will see "Car:Cockpit". Click on it.
3.Go to "Verticies 181"
There you will find 181 points described by means of three axes: X,Y,Z.
X - you move the points from left to right.
Y - you move the points up or down
Z - you advance or retract the points
You just change these points (verticies) by clicking on them on the preview screen or manually, by applying certain values yourself on the left.
The most effective method to comprehend cockipt edition is "trial and error" method. Just stick at it and one day things will get brighter. What I remember is that point (84) is a cockpit view steering wheel while points (3) and (4) are the front wheels seen in the cockpit.
If you want to deal with the antenna, I suggest that you downloaded the cockpit with antenna and tried to edit its shape.