System account password in Exchange 5.5

Here is the scenario: 4 exchange servers under one domain. One on PDC the others three on BDC’s at remote sites connected via VPN so they do not use connectors. All the servers think they are under one building. They are under the same site name. Ineed to change the “system” password since it is a weak one.
For all your Exchange gurus, what is the BEST and safest way of changing the password? Do I need to go to user manager and then to the exchange servers? I’m not too sure what to do or how to do it without causing major issues. Any help would be appreciated.