To reset your password via OWA, navigate to the OWA login page, and enter your current username and password.
From the Tools menu, select Options.
From the left hand navigation menu, expand the General category, and select 'My Account'
On the 'My Account' page, click the button.
In the Change Password form, enter your old password in the 1st field, and your desired new password in the 2nd and 3rd fields, then click 'Save'