You can: 1) Use an antivirus (there are even online scanners, if you don't wish to install it) 2) Use a remover (you have to know what virus you want to remove) 3) Remove it manually, by deleting infected files and virus-created registry keys (you have to know what are you doing, or you can cause more damage than the virus itself) 4) Format and reinstall windows (you will lose your programs and settings, and even your data, unless you saved them on a different partition, so do this only if you are desperate)