How change model?

Hello, I’m new to the game and I’m having a problem. Namely, I can not change the model.
More specifically, I invented a compact model and wanted to make a new vehicle, but I don’t know where I can determine it. please help.

You can’t change the body type of an existing model, but you can clone them and then make changes to the clone. Use the ‘create similar model’ button.

Each time you research a new body type, one model is created for that body type (in your case, there will be one for the compact body type), and if you want more models of that type, you must clone it.