"Tú no cambiaste mucho."
Translation:You didn't change much.
My sense is that "no has cambiado" means you personally haven't changed much. Whereas "no cambiaste" refers to something you did---like redecorating the house.
It is only wrong technically. While 'you didn't change much' is a better word-for-word translation, the phrase 'you haven't changed much' is more natural English phrase