Login at Customer Control Panel with your email address & current password.
Click on the Login link.
You'll see a Change Password button, click the button.
Type in your Old Password.
Type in the new password you want use.
Verify the new password, then click Submit.
If you don't know what your old password was, you'll need to contact the person who setup the Hosted Exchange Account for you and they'll need to reset it for you.