how to reset my iPhone password

Your Apple ID password or the phone passcode?

If you forgot the Apple ID password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get a Rescue or Notification email option if necessary. Link to contact Apple Support at the end of the 2nd article.

Apple ID - Manage            

Apple ID – Forgot Password            

Passcode

Passcode - If you forgot the passcode for your iPhone or your device is disabled.