How do I Uninstall Windows Security Defender?

It is the Most Irritating software EVER! It somehow got onto my Computer through means unknown, and gives me a Pop-up every two seconds, that I have like 500 Viruses and Malware etc, but I know it is not true, because I scan my Computer regularly, and I have no Viruses. How do I delete it? If you know, can you give me the File Directory so I can Annihilate it.