Vlk
2
campman,
depends on what “variety” of Professional you have on your mind.
-
if you mean normal commercial version, it’s ultra-simple: just insert the Pro key to the installed avast! Home Edition; it will be automatically recognized and avast will instantly upgrade itself (requires working Internet connection). 
-
if you mean the trial version, you’ll probably have to uninstall the Home version and then install the Pro.
Hope this helps,
Vlk