As Borg 386 says there are many good free anti-virus programs out there. MSE is one a lot of people use. Follow the link and make a choice thats relevant to you. Just make sure that if you DO switch to another, ANY other , that you completely remove all traces of the one you're using now. Thats very important!
You didn't mention what kind you are using at the moment but just search "how to uninstall *****anti-virus" and follow those instructions. I don't switch very often as I've found one that works for me (free), but the last time I did , I used REVO uninstaller to remove the last one. (use the advanced tab) Its free too. Most any of the top tier free anti-virus free editions are decent enough, but get an on demand scanner too. I recommend Malwarebytes and/or Superantispyware. (again. both have free editions and are the ones I personally use)