Changes here are only necessary if advised by you internet service provider.
A Domain Name Server (DNS) is an index of IP addresses and Web addresses.
If you type a Web address into your browser, such as http://www.iinet.net.au/,
a DNS server will find that name in its index and find the matching IP address: xxx.xxx.xxx.xxx.
Most ISPs provide a DNS server for speed and convenience.
Since your Service Provider may connect to the Internet with dynamic
IP settings, it is likely that the DNS server IP's are also provided dynamically.
However, if there is a DNS server that you would rather use, you need to specify the IP address here.