support.avast.com › article › Install-Free-AntivirusHow to install Avast Free Antivirus on Windows | Avast Download Avast Free Antivirus for Windows Right-click the downloaded setup file avast_free_antivirus_setup_online.exe and select Run as administrator from the context menu. If you do not see the Run as administrator option, refer to the following article for instructions to manage administrative accounts on your PC: