When it comes to deciding “what episode does Sasuke become good”, different anime lovers have different opinions as to when this change actually happens some even believe that he was never “bad” in the first place and everything he did, he did it on some solid reasonable grounds, as this was part of his upright character and personality. But something that all of us can agree on is that he was one of the greatest and powerful ninjas of all time and he actually has reasons to do whatever he does, usually.
Now if we actually dive deep into the story and consider things to be black and white, good and bad, regardless of Sasuke’s point of view about all this and take, being on Naruto’s side is considered as “good”, we can say that Sasuke becomes good after his epic last fight with Naruto during the 478 and 479 episodes, which actually happens because Sasuke reveals that he aspires to become the Hokage of the village and for that, he needs to get rid of anyone who stands in his path, that includes Naruto as well.
But after the intense fight between two of the greatest rival ninjas which end up with Naruto managing to beat Sasuke, who just couldn’t match Naruto’s Chakra. Naruto later talks some sense into Sasuke, who realizes that he is wrong and from this point on becomes actually, what people refer to as “Good” but then again it is totally up to how one perceives certain elements in the anime series.