1. Click the Apple menu in the upper-left corner and select System Settings.
2. Select Wi-Fi from the settings on the left, scroll down on the right and click Advanced.
3. Under the Known Networks section, find the network you wish to remove and click the circle with three dots in it.
4. In the window that pops up, click Remove From List.
5. Click Remove in the confirmation window that appears.
6. Repeat the above process for any other networks you wish to remove.
7. Once you have finished removing networks, click Done.