The MultiRes modifier reduces the memory overhead needed to render models by decreasing the number of vertices and polygons. This is useful not only within 3ds max but for game and Web content creators who export models for use outside of the program. MultiRes offers several advantages over the Optimize modifier, including faster operation and the ability to specify reduction as an exact percentage or vertex count.
The MultiRes modifier now supports the preservation of map channels when face count is increased or reduced.
JUST GO TO HELP, AND TYPE IN MULTIRES, IT WILL SHOW YOU HOW TO DO IT ;D