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