There is an empty above the model that all the objects are parented to for moving the entire model around. It is on a separate layer below the model layers. All the objects are also grouped in a group called parking garage for bringing into your existing scenes more easily. There are two scenes  a day scene and a night scene which you can switch between with the scene menu at the top menu bar. If you want the night scene darker, I would suggest turning off ambient occlusion and turning down the strength of the sky. You can also adjust the light emitting shaders to emit less light which will create darker pools between the lights. There are 4 light emitting shaders. Two for the daytime scene and two for the night time scene. The daytime scene shaders are called lightOff and lightParkingOFF. The night time scene shaders are called lightParkingON and lightON. The scene is currently set to simplify with the setting at 1 subdivision. Render times Currently there are a number of shaders with bump maps and varying degrees of reflectivity. These two things make the parking garage look a lot more realistic but at the cost of higher render times. If you want the scene to render faster, you can go into the shader nodes and disconnect the bump maps from the displacement socket on the material output node, and connect the diffuse shader directly to the material output node instead of going through the mix shader that adds in the reflectivity.