I really don’t know what’s so complicated about it.
If you go to our web pages and browse e.g. through Support / FAQ avast! / Installation/Uninstallation - avast! uninstall untility is the very first link. Alternatively, you can use the “Download” menu and select avast! uninstall utility. What easier way can there be??
(Btw, you probably don’t need this tool at all - the ordinary Control Panel / Add/Remove Programs should work just fine.)

Don’t know how you came to the conclusion that you need another “avclean4” tool…