If you have un-needed wireless networks listed in the Windows 8.1 GUI you will have to open up an Administrator Command Prompt to manually remove them.
Press Windows + X on the keyboard and then click on Command Prompt (Admin).
Enter the following command to display your saved wireless networks:
netsh wlan show profiles
Next delete the desired profile. For example to remove the “PricklyG” network pictured above:
netsh wlan delete profile name="PricklyG"