HOW DO I REMOVE THIS SECURITY APP?

I HAVE NO IDEA HOW THIS ATTACHED ITSELF TO MY FACEBOOK BUT BECAUSE OF IT I HAVEN'T BEEN ABLE TO GET INTO M FACEGOOD FOR 2 DAYS.  IT TELLS ME " YOUR COMPUTER NEEDS CLEANING" ON THIS PAGE THE ONLY OPTION IS TO LOG OUIT DOES HOWEVER TELL ME I CAN USE FACEBOOK WILL CLEANING BUT DOESN'T OFFER A LINK TO GET INTO MY FACEBOOK.  SO WHEN I CLICK "LOG OUT" IT AGAIN ASKES ME FOR MY USERNAME, WHICH IS MY EMAIL ACCOUNT, AND PASSWORD..WHEN I ENTER MY USER NAME IT IS COMING UP AS SOMEONE ELSES.  SO I NEED TO CHANGE MY PASSWORD AND ALL 8 TIMES I CHANGED MY PASSWORD, IT SASYS INCORRECT PASSWORD.  NOW I DON'T EVEN HAVE A PASSWORD.  HOW THE HELL DO I GET RID OF THIS NEUCENT SITE???   OH, WHEN I CLICK ON DOWNLOAD" IT STALLS AND KEEPS ON TRYING TO INSALL AND NEVER DOES.