Change Central Administration port number in SharePoint 2010

1- On the Start menu, click All Programs.
2- Click Microsoft SharePoint 2010 Products.
3- Click SharePoint 2010 Management Shell.
4- At the Windows PowerShell command prompt, type the following command:
               
                    Set-SPCentralAdministration -Port <PortNumber>

     Ex- Set-SPCentralAdministration -Port 30217


Note : The Set-SPCentralAdministration cmdlet blocks the following ports:
           Lower than 1023
           Higher than 32767
           443 (SSL)

1- If you want to set the Central administration port to a port below 1023 then run the below command in Windows PowerShell command prompt
                 stsadm -o setadminport -port 81
2- Reset the IIS.
                 iisreset -noforce