3D MAX RENDER PROBLEM

DEAR ALL MY FRIENDS ANYBODY HELP ME IN 3DMAX IMPORTING AND RENDERING.. I ALWAYS DO IMPORT-MERGING FILES FROM EVERMOTION LIKE THE TREES, SOFA AND ETC.. THE PROBLEM IS I DONT KNOW HOW TO DECREASE THE VOLUME OF FILE IN MY SCENE SINCE MY SCENE BECOME BIGGER VOLUME AND HARD TO RENDER,VERY SLOW..I WANT THE FILE CONVERT INTO VERY LOW BUT REALISTIC WHEN IT RENDERED BEFORE I MERGE TO MY SCENE.. ANYBODY HELP ,KNOW THE PROPER PROCEDURE? THANK YOU