To change your password in the Office 365 portal.
1. From a browser sign in to your Myprofile account from https://myprofile.microsoft.com/ page.
2. On the MyProfile page
a. Select Password from the left navigation pane
3. On the change password page:
a. Type your old password.
b. Type new password.
c. Confirm your new password.
d. Click Submit.
For additional information please see How to create a secure passphrase