Avast will not quit

My internet suddenly and without warning became extremely slow, so I suspected a virus. I downloaded what I assume was a demo version of avast for mac. I’m not sure exactly what version of avast I have, but it’s probably the most recent. I ran a scan in safe mode and everything was fine until the scan completed. Avast constantly opens “Mail” and Avast itself will not quit. It also automatically reappears whenever my computer starts up. Force quit and restart obviously aren’t working. How do I quit and/or uninstall avast? I don’t know if it matters, but avast did not find any viruses, and the slow internet issue has been resolved somehow.

In the avast preferences you must uncheck “Launch at startup as a persistent application” before you can quick the avast service. Once you quit the application you can reboot your Mac and then drag the avast .app to the trash if you wish to remove it