What does it mean when you change your act?

Answer 1

When someone tells you that you need to change your act, they are trying to tell you that you are behaving in a way that they find offensive. And/ or it could mean that you are indulging in self destructive behavior and they want you to stop. They are also telling you that they have seen this 'act' before and again they are asking you to change your current behavior/ attitude.

Answer 2

It depends, perhaps it means to change how you present yourself, act, speak, or treat others.