In Office 365, you can do a password reset before password expiry (90 days). Resetting your password this way will give you another 90 days from reset. You can use this method to change to a new password at any time, if you get tired of your current password or you think it may have become compromised.
Steps;
1. Log in to Office 365: https://portal.office.com
2. Look for the settings icon in the toolbar at the upper right. The settings icon looks like a gear. Click on the Setting icon and look for the "Password -- change your password" Option. Click on this option.
3. You have reached the "change password" screen. You can change your own password here.