In order for you to change your hosted exchange mailbox password, logon to your webmail at:
http://webmail.yourdomain.com or https://postoffice.entirelydigital.com
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.