If you are the Simplehost account holder you can login to your My Account and click E-Mail Admin.

Users can login to change their Mailbox Password in the users section.

https://simplehost.co.nz/mailadmin/users

Login with your Mailbox Username (your email address) and Password.  These will be the same login details you use with Webmail or your E-Mail client.

If you need to reset this password please contact the account holder, or contact support.