To change your password in Outlook Web Access (OWA):
First log into Microsoft Office 365 (https://www.office.com)
Then navigate to the Settings Gear icon at the top right of your screen
Click on Change Your Password link, located on the left side of the screen

On this screen, you will need to type in your current password in the “Old Password” field
Then type what you want to change your password to in the “Create New Password” and “Confirm New Password” fields

Click Submit at the bottom of the form
Once saved, you will then be logged out and you will need to go to office.com and log back in with your New Password you just set
When you get logged back in, click the OUTLOOK logo on the left side of the screen
If you get back to your inbox, you have completed changing your Office 365 (including Outlook) password. You will use need to use this new password to log on from now on