The passive form 'I've been changed' focuses on what or who has changed you. For example: 'I'm not the same person that I was a year ago. I've had a lot of bad experiences since then, and I've been changed by them.' The statement 'I'm changed' is a little odd if you are intending it to be a passive. If you are using a passive to talk about a change that has happened in recent time and which impacts on how you are now, you would need a present perfect form. And if you are simply describing the state that you are in now in the present tense, the sentence wouldn't be a passive. 'I am' is simple present, and 'changed' would be interpreted as an adjective meaning 'not the same'. In fact, the most natural statement to make in this situation would be 'I've changed'. If it's not relevant what changed you, or you want to suggest that the changes are a development which just happened naturally, you would say 'I've changed'. This simply means that you are not the same as you were before.

the first one is the passive form of Present perfect and the second one is the passive form of present Indefinite