I don’t remember my passWord

If you mean your Apple ID password→If you have forgotten your Apple ID password – Apple Support

If you mean your iPhone unlock passcode: See this Apple support link→If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

Or watch this companion video ⬇️

What did you forget? If you forgot the passcode to unlock your phone, use the related article link at the top of the page. What do you mean by changing the password user name?