I somehow got Win Anti Virus Pro downloaded on my computer. Now Iam getting pop ups every 5 minutes. How do I?

take it off? I have tried to download free antivirus programs....didnt work. I have spybot and that dont even work. Is there a way I can manually take it off?? It is driving me nuts.As you can see, Iam a tad computer illiterate. Thank you for your help.