How to upgrade from Avast Home to Avast Professional Edition?

In order to upgrade Avast Antivirus Home Edition to Professional Edition you'll need to uninstall the Avast Home first.

When the Home Edition is completely uninstalled, go to Avast Online Store, purchase your Avast Professional Edition license, download the installation file and install the application as normal.

You'll be assigned with the serial product key that is sent to your email address. Take great care not to lose it because it will be needed during product download and activation.

You can enter the license key by right-clicking the Avast tray icon and then the About avast! option. Then click the "License key" button and provide your license key.