In order for you to change your hosted exchange mailbox password, logon to your webmail at:
your username is your email and your password is the current password assigned to you by your administrator
Once logged on, click on the options button at the top left:
Then click on "Change password in the left menu:
Enter your current password, then your new password twice and click the save button:
That's it, your new password has been saved. You must now use this same password on your mobile device, Outlook and web access.