To change the password for each mail account, do the following:
1. Go to http://www.servermx.com/en/login.html
2. Log in with the email address and password you gave them
3. Click on "Edit mailbox" in the left-hand column
4. Write the "Password" and "Confirm password" fields with the desired password for the email account
5. In order to confirm any changes Click on "Submit"