Click on the WiFi icon in the upper right hand side of your computer screen:
Scroll down to the bottom of the dropdown menu and select "Open Network Preferences..."
From this screen, click on the "Advanced" button in the lower right hand corner:
Then select DNS:
Then click on the Plus symbol and add the following
to the list of DNS servers. Once you've entered the first entry, click the plus symbol again to add the next. Once complete, Click OK
On the next screen, click "Apply"
Then click on this link to test your new settings.