Changing SMTP Port

[Mr20]

I am in the process of installing Symantec Antivirus for SMTP Gateways on my companies server. The instructions say to assign The Symantec Antivirus SMTP Gateways to listen on port 25. Currently my W2K Exchange Server is assigned to that port.

My question is how do I change the port that the Exchange Server is assigned to, so that I can assign the Symantec Antivirus SMTP Gateway to port 25.

Thanks in advance for your help.