Corporate email addresses used in MyCentury.ca and MyBria.ca (Jostle) are managed through Google Apps.
To change your password, log in at myaccount.google.com using your Jostle login and password.
Scroll down to the SIGNING IN area and click on PASSWORD.
In the window that opens, type in your new password in the two fields and then click the CHANGE PASSWORD button.
Note that this will change your password for all corporate services using Google Apps. Currently, this is limited to Jostle and email for a small number of users, but the list will grow in future.