How to Delete a Wi-Fi Network

  1.   From Apple Menu go to System Preferences





  2. Go to Network



  3. Select Wi-Fi  


  4. Click Advanced...



  5. Select UCSD-GUEST from the list




  6. Click the Minus ( - ) button 





  7. Select OK.   






    8. Click Apply 



Apple's Support page - How to forget a Wi-Fi network on your iPhone, iPad, iPod touch, or Mac

https://support.apple.com/en-us/HT208941