So in the first screenshot, I want to remove this light bar, but when I do, It removes other parts that I would like to keep on the model (second screenshot). How can I only remove the light bar and not the back emergency lights?

Alt+f4

Polygon mode, click the object, then click quadr, then right click and drag the box on the selected area you want to delete. Then once its all red, click delete. I also suggest you isolate what you want to remove. There are some pretty good tutorials floating around as well.

Polygon mode, click the object, then click quadr, then right click and drag the box on the selected area you want to delete. Then once its all red, click delete. I also suggest you isolate what you want to remove. There are some pretty good tutorials floating around as well.

Not really following ya..

Not really following ya..

 

Since you're new to Zmodeler, try the Zmodeler 2 forums. A lot of tutorials will help a lot there.