simplifying a 3d model

Hello, is there a way to simplify a 3d model with many details in it to a point that all that is left is only the most upper layer of it with without doing it by hand?
thank you .

This functionality is not build into Unity.

The Asset Store does provide a few packages to simplify meshes though:

If you use Blender it offers a Decimate Modifier. I find it works well for certain meshes (mostly quads). I have reduced face count by more than 60% without much noticeable difference. And it even preserves UV maps pretty well.

thank you !!! can it handle cases like having a car model (for ex.) with seats, engine, and alot of details inside the model? i mean- is there any software that can delete the inside of the model without harming the outside?

Just segment your models/meshes onto different layers and work on the individual pieces, later just combine all the layers.