How to change DNS server in a remote machine
Download regfind.exe from here .Extract the zip file .Browse to the extracted location from command prompt and run the utility using the following syntax
regfind -m \\computer1 -p HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\parameters "Old DNS IP" -r "New DNS IP"
Where Cumputer1 can be the name or Ip of the remote machine whos DNs is to be changed
Once the command completes successfully, the old dns IP in the server will be replaced by the new one