i need to change the dimention of the design after finshing the drawing from mm to cm ???
While editing your drawing go under the manage tab and choose the styles editor. It'll be in the styles and standards section. Now you want to expand the dimension section on the left side and click on the default that you are using (probably default - mm). From here you can change all the units in your drawing. This is for Inventor 2016 so depending on your version YMMV.