Apache webserver will show documents that are put to a specific location. Root of that location is referred as document root.
For example, if DocumentRoot were set to /var/www/html
then a request for http://www.yoursite.com/folder1/yourpage.php
would result in the file /var/www/html/folder1/yourpage.php
being served to the requesting client
In ubuntu default location is /var/www
for server root and on Centos its /var/www/html
This change requires a service restart.
you can change this from /etc/httpd.conf
where there is a section about document root.
But again on your distro which is ubuntu its under /etc/apache2/http.conf
Debian based systems
ServerRoot :: /etc/apache2
DocumentRoot :: /var/www
Apache Config Files :: /etc/apache2/apache2.conf
:: /etc/apache2/ports.conf
Default VHost Config :: /etc/apache2/sites-available/default,/etc/apache2/sites-enabled/000-default
Module Locations :: /etc/apache2/mods-available, /etc/apache2/mods-enabled
ErrorLog :: /var/log/apache2/error.log
AccessLog :: /var/log/apache2/access.log
cgi-bin :: /usr/lib/cgi-bin
binaries (apachectl) :: /usr/sbin
start/stop :: /etc/init.d/apache2 (start|stop|restart|reload|force-reload|start-htcacheclean|stop-htcacheclean)