HOW do i remove the fake windows defender??!?

Somehow the fake windows system defender got installed on my PC, and its driving me crazy and keeps telling me i need to purchase it to stop the warnings, every MINUTE i get another popup from it and ive tried to remove it with so many programs and it hasnt worked, its slowed my PC and every time i click something on my PC or desktop it says i need permission from the administrator user, but i only have one screen and i AM the administrator user, so i cant do anything on my PC anymore! ive also used spybot search and destroy, and iv used malwarebytes anti-malware, and its still on my PC. HOW do i remove this nuisance damnit hah