When you're talking about the act of changing, you have to say "It has changed" (and you're talking about the time that it changed). But if you say "It is changed", you are talking about the state after the act of changing. For example: The policy has changed (referring to the time that it changed).

Has been changed or has changed?

You can generally use both of them,as they are both grammatically correct,but,in short," has changed" is a way of stating that a change has occured,while " has been changed" implies that someone or something has made that change.

Is has changed passive voice?

Is changed uses the passive voice. It's a way of reporting on the state of the thing you're talking about. "Has changed" would have the same meaning, but it uses the active voice instead. If the subject performs the action, we're using the active voice.