Are you trying to go through the official removal process to get rid of Sophos Antivirus from Windows computer?
You are supposed to switch Avast from Sophos Antivirus. However, Avast can't be installed without uninstalling Sophos first, and you are failed even though you dragged it to the trash and emptied the trash. And it still can't install until you delete Sophos from your computer.
Take it easy! You could learn and follow Sophos Antivirus uninstall tips in this article.