how can I uninstall Norton antivirus from my iMac running EL Capitan?

The Norton Antivirus version I had prior to updating to EL Captian does not work with El Capitan, apparently. I want to uninstalled and use instead Symantec Endpoint Protection (which by the way I have been told works better than Norton).

When I tried to install Symantec the computer says that there is another antivirus program in use by my computer and because of it can not install Symantec. I have tried to go to the applications folder and drag into the trash the Norton Virus folder, then empty the trash and even do so and then restart the computer. I have every time the same result, obviously I am missing something because the program is not quite uninstall (it show in my desktop upright corner.. Any ideas?

Thanks