Game modelling how to get height details? I am trying to create a model for unity 3D.

To my knowledge blender - Normal map  is only going to smoothen the edges 

Now how the height details are passed? What kind of texture is required? 

I have a high poly model and low poly model, is there a way to do it?
I am not too sure about Unity, but in blender the usual way to go from highpoly models to lowpoly models is to create a normal map from the highpoly and apply it to the lowpoly. To do this see here:
https://www.youtube.com/watch?v=BOYRCI-dtjU

Hope it helps :)