how move my itunes library from old external harddrive to a new bigger external harddrive

i have my itunes library on an external hard drive but now i want to move the itunes library over to a new bigger external hard drive . i just got a new imac and I want to keep my music and movies content on off my imac. I finally just got my imac itunes to recognize the old external hard drive but now I want to move to the new 2tb harddrive. Any help would be appreciated