The basic concept of discrete LOD (DLOD) is to provide various models to represent the same object. Obtaining those models requires an external algorithm which is often non-trivial and subject of many polygon reduction techniques
https://graphics.stanford.edu/courses/cs468-10-fall/LectureSlides/09_Progressive_Meshes.pdf
Simplification is made using Edge collapse algorithm
Complexication is made using Vertex split algorithm