"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
I guess it depends on what you are trying to say. I'm not sure what this sentence really means. It's hard for me to think of a situation where I would say "You didn't change much." "You haven't changed much" is certainly a common sentence, and I can even think of situations where I might say "You hadn't changed much." But off-hand I can't come up with a situation where I would say "You didn't change much." I'm sure someone will come up with an example.