[support] setting.php

[c cc]

My drupal installation is under a subfolder of my domain; therefore, I
need to type the subfolder (www.example.com/drupal) on the address bar
inorder for drupal to come up. How can I change the setting so I do
not need to type the subfolder, like www.example.com instead of
www.example.com/drupal?

I have tried to change the settings.php $base_url
='http://example.com' instead of $base_url
='http://example.com/drupal', but it still does not work. Any idea?
Thanks!