Change Exchange 2016 Mailbox password in OWA
Log into OWA by going to
On the top right corner, you can click the SETTINGS icon and select the OPTIONS.
On the left menu, go to GENERAL and then MY ACCOUNT.
On the bottom right, there is a link for CHANGE YOUR PASSWORD. Select that.
Then a new dialog box pops up on the right side. Enter in the current password and the new password twice. Select SAVE to complete your password change.