To change a port number that SharePoint Central Administration site is running on:
- Open Command Prompt
- Go to BIN folder in SharePoint install directory (by default, it would be "C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN")
- To get the port number that Central Administration site is currently running on, type
stsadm.exe -o getadminport
- To change a port number that SharePoint Central Administration site is using, type
stsadm.exe -o setadminport -port <portnumber>