Malwarebytes and the free version of AVG anti-virus have not failed me.

Start with Malwarebytes. If it finds malware, run it multiple times until it comes back with a completely clean report.

You may find that malware already infecting your machine will prevent you from going to the website to download it or installing it when you do. Last time I had to download the install files to a USB drive on another computer, then rename the .exe file to a .bat because the infections were blocking all .exe installations.