Where can I change the default directory?

[rokmakovec]

I have the index.php file in /var/www/html/data/Sola, but when i login i can see all stuff from /var/www/html/ but i wanna to see only /var/www/html/data/Sola

[prasathmani]

$root_path = $_SERVER['DOCUMENT_ROOT'].'/data/Sola';