Wireless: Delete a Wireless Network (Mac OS X+)

How to Forget a Network (Mac OS X):

1. Open System Preferences.

2. Select Network within System Preferences.

3. Choose Wi-Fi (Option on the left)

4. Select Advanced...(Located near the bottom right)

5. Select the Wi-Fi Network to remove.

6. Select [ - ] beneath Preferred Networks Box to remove network.

7. Select OK and close Network preferences. Click Apply changes if prompted.

Referenced from: tp-link.us