Forgetting a Wi-Fi network is a helpful step in troubleshooting issues with your network connection. Forgetting a network will not prevent you from connecting to it in the future, though you may be asked to reenter your credentials.
NOTE: You will need administrator rights to your machine to perform this action.
Open System Preferences.
Uncheck Automatically join this network.
Highlight the network you want to forget.
Click the Minus (-) button.
Click the network icon from the taskbar.
Right-click the network to forget.
Click Forget from the drop-down.
iOS (iPhone and iPad)
Navigate to Settings.
Tap the info button next to the network you want to forget.
Tap Forget This Network.
Slide the Quick Settings Drop-Down menu from the top of the screen.
Tap the gear icon from the top right of the screen.