In order to change or reset your password, you will first need to log into Office 365 https://portal.office.com.
If this is your first time, you will be prompted to confirm your current password:
Then you will be prompted to pick one of two authentication methods:
You will then receive a numeric code from whichever authentication method you chose; enter that code and you are done.
You will not be prompted again, this is a one-time authentication process.
If you forget your password, you will have an option to click “reset your password” which will bring you to this screen:
To simply change your password you will login to office 365 and in the upper right hand corner you will see this:
Select the “cog” to change your password.