Two Antivirus?

I have the SBC antivirus but it doesn't really do much and doesn't delete my viruses so I downloaded a free one, but when I was installing it it said that having two antiviruses could create system problems. I don't really want to uninstall the sbcone, but is it safe to install the new one. The new one is called bitdefender antiviris if that helps. Also, do you think I'd be better off going to a store and getting one. The viruses that I have don't sem to be doing much, but I'd like to get rid of them anyway.