You need to configure the /etc/network/interfaces file if you want to change your DNS server via the command line.
If you have more than one DNS server, just add a space between each:
dns-nameservers X.X.X.X Y.Y.Y.Y Z.Z.Z.Z
Just replace the X’es with your own IPs and the DNS server of choise, and when this is done, run this command to update the settings:
sudo ifdown eth0 && sudo ifup eth0