First things first, in order to change DNS settings internet is must else there will be no server to change at all.
Changing DNS Settings in iOSModifying iPhone DNS settings is almost similar in all iOS devices and versions. Although you might find little difference in user interface but basic steps are same. Let us follow the step by step procedure :
1) Go to “Settings” locate the Wi-Fi option and tap on it.
2) From the list of available wireless connections select yours and then tap onto (i) button found to right of router’s name.
4) Exit “Settings” by tapping on the back button.
That’s it! We’re done. In order to make the changes effective it is likely that phone needs to be re-booted by switching it off or else the phone might still pick up old cached DNS settings.
How to Know What DNS Servers to UseDNS servers are picked up automatically by Wi-Fi routers through DHCP and the DNS is pulled from specific Internet Service Provider and an address like “192.168.0.1” could be seen. So if your phone needs a speed boost up it can be switched to a faster DNS.
If you are unsure of DNS servers to use you can choose from ISP provided addresses or even public DNS services. Few of these public DNS IP addresses are listed below.
Google Public DNS IP addresses: