I assume you have changed the order of the DNS entries in the Network preference pane and it didn't change anything?

Try changing the order of the DNS entries in the Network preference pane:

1. Open System Preferences → Network.

2. Select your network service in the list on the left.

3. Unlock the preference pane using the lock in the bottom-left corner.

4. Click Advanced… and choose the DNS tab.

5. Change the order of the DNS servers by dragging them up/down.