Or take a look at those tutorials:
3ds :
blender:
But instead of using a generator/modifier I would recommend you to decrease it manually -> so that you have full controle over the lod creation process (but some gen/modifiers are pretty good) 
Or take a look at those tutorials:
3ds :
blender:
But instead of using a generator/modifier I would recommend you to decrease it manually -> so that you have full controle over the lod creation process (but some gen/modifiers are pretty good)