Changing your DNS settings on your Mac can be done in a few short steps.
1) Launch the System Preferences app on your Mac (under the Apple in the top menu) and open the Network preferences pane.
2) In the next interface, which shows your internet information, click on the Advanced button at the bottom of the interface.
3) A drop-down interface will appear. From here, open the DNS tab and then click on the + button under the DNS Servers list.
4) After clicking the + button, you’ll begin typing the IP address or domain name of the DNS server you want to use. We’ll be using Google’s public DNS server, which is 188.8.131.52
5) Once satisfied with the entry, press the Return key on your keyboard, then click the OK button, and then click the Apply button to save your changes.
6) If adding 184.108.40.206 still doesn't work. Try adding 220.127.116.11 as an additional DNS server and repeat step 5.
And you're done!