I want to enable file listing index for some directory in my domain.

(ex. aaa.com is disable but enable only aaa.com/downloads)

Can I do this on WebUI or I have to edit /etc/apache2/sites-enabled/ispcp.conf manualy ?

Thanks,

This is not possible with the GUI. Save a file called .htaccess with the following content in this directory:
For more information about .htaccess read the apache documentation: http://httpd.apache.org/docs/2.2/howto/htaccess.html