Remove any antivirus program (Norton, AVG, Command etc....). You do not need to remove old version of Sophos
Download Sophos , click on this link (Save this file on your desktop) Double click the file "Windows_Sophos_install.exe"
Click RUN to begin the install - this may take a moment to start DO NOT CLICK IT AGAIN - This will take a while to start.
Once you see this logo in your tray you can consider your install complete.