If your Office 365 account is a purely cloud-based account - in other words, if it's not synchronized with your local Active Directory - use the following steps to change your password:
- Sign in to Outlook Web App (http://mail.office365.com)
- Click on the Settings gear in the upper right of the screen, next to your name
- Choose Office 365 settings
- Click on the Password section on the left
- Enter your old password, then enter a new password and confirm it. You will be required to enter a strong password - the page will let you know if your password does not pass muster!
- Click on Save
Keep in mind that you will be prompted for your new password next time you use your desktop version of Outlook to connect to email - and you will also need to update your mobile device with the new password (you should be prompted to do so next time your device checks for email).