Also see: Revert DNS Servers back to DHCP on Windows
- Apple Menu -> System Settings 
- Network 
- Wi-Fi (may need to do this on Ethernet connection(s) as well) 
- Details 
- Highlight any manual DNS entries, and click the - to remove them.  Once all manual entries are removed, the dynamic entries remaining will be grey and you will not be able to remove them. 
- Click OK
