To back up IAS Server, RDP to the IAS server, open command prompt and type netsh aaaa show config > path\backupfilename.txt
Copy the file you created to the new IAS server.
On the new server open command prompt and type netsh exec path\backupfilename.txt
A message appears indicating whether the update was successful or not.
There is no need to stop the IAS on either of the server.