In 4.x, you cannot update DNS information by going to port 5480 (MAIPAddress:5480).
 

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1. You need to do the following: Login to your ELM As root:-
2. root@localhost ~ # cat /etc/resolv.conf (This step will give server list that you have configured)
3. root@localhost ~ # nano /etc/resolv.conf (This step will allow you to edit resolv.conf file).
4. nameserver (Enter DNS server IP here)
   Ctrl + k to delete any entry from resolv.conf file
   Ctrl + U to Uncut/Undo any entry accidentally delete from resolv.conf file
   Ctrl + x to Exit from resolv.conf file
5. Confirm - Yes
6. File Name to Write: /etc/resolv.conf - Enter.

If this does not work. Edit the ifcfg-eth0 file here:

nano /etc/sysconfig/network-scripts/ifcfg-eth0

Change or remove the DNS= lines that point to the old DNS servers. Removing the DNS lines should revert back to the changes in /etc/resolv.conf. Changing the DNS addresses in ifcfg-eth0 will also work.