I have look in the FAQ’s of avast and mayby is the follow instruction the solution because I don’t find the control panel also not in "start>settings.

"avast! uninstall utility
Sometimes it´s not possible to uninstall avast! standard way - using ADD/REMOVE PROGRAMS control panel. In that case you can use our uninstallation utility aswClear.

How to uninstall our software using aswClear.exe:

Download aswClear.exe on your desktop
Execute it
If you installed avast! in different folder than default, browse for it. (Note: Be careful! The content of any folder you choose will be deleted!)
Click REMOVE
Restart your computer"