Step 1: Once you login to the Office 365 portal click on your profile photo or icon beside your name from the right top corner of the browser.
Step 2: Click on ‘My Account’ as shown in the picture below
Step 3: In the My Account page click on ‘Security & Privacy’ from the left menu.
Step 4: Click on the ‘Change Password’ on the ‘Security & Privacy’ page.
Step 5: Then follow the instructions on the screen.
Step 6: If your company’s Office365 account is being synced with your Active Directory or any other Identity management service, then the process will be different. In those cases, you will get a warning or notification that you cant change the password here.