To change your password just log in to web mail, if your password does not meet the strength requirements you will be prompted to change it.
What if I don’t know an existing password?
If you don’t know the password for a inbox you can reset it by logging in as the main email admin for your account.
To login as the main email admin go to http://mail.storesecured.com
the username would be email@example.com
If you don’t know the password for the managedomain inbox there is a link to have it emailed to you from general–>email–>setup instructions.
Once you are logged in as the main email user you can reset anyone’s password. Go to settings–>domain settings–>users. Click on the check box for the user you want to change the password for and then click edit. From there you can enter in a new password.
What if I’m not using the inbox?
If you do not use a particular inbox you should delete it by following the instructions above except choose delete instead of edit for the user you want to remove.