They really aren’t that hard. Just make the various versions with more or fewer polygons.
Import the base that is the highest Poly version you want to be your hero object > Open it in the Mesh View > Details panel on the right > Under LODs > Import LOD1.
You can have up to three other LODs. There is an auto feature that will calculate it for you or you can choose to set the distances yourself.
It’s a fairly simple process that can have great performance gains. If you end up having questions regarding it feel free to ask anytime! 