Change apache2 web directory

You want /etc/apache2/sites-available/default (assuming you want to
adjust the default site for your server). Replace the "/var/www" with
the path to your website. It can get a lot more complex than this but
that's the easy way.

For peace of mind, it might not be a bad idea to backup the original
file before you start making changes. After you're done I think you
need to restart apache - apache2 -k restart.