What is the best and easiest way to make a size 4t dress pants into a size 2t dress pants?

Any links or detailed answers would be greatly appreciated. I am not a fantastic sewer but i know my way around a sewing machine and i sew quite often, but I have never tried to resize pants. They do have a button and a zipper. They feel like a polyester blend but they do not have a tag. They are just like mini tuxedo pants.