How you change the main greeting is to access the administrator mailbox and use the admin password. Unfortunately, forum rules prohibit passwords from being posted here. I trust that you understand the need for this position.
Your 1st route should be to contact the vendor who installed your system or another local STSe vendor. For one of us to help you would require a verified letter of authorization from the owner of your company and/or a pre-pay of a small fee on a company credit card. We just can't blindly give out system passwords.

- Dave S. -

You can never appease your ideologue opponents.