If you not have access to the php.ini file you can try to edit your htaccess file. (You find this file in the root of your Joomla! installation. If the name is htaccess.txt, remember to rename it to .htaccess .
Write this to your .htaccess file
# supress php errors php_flag
php_flag display_errors off php_flag html_errors off php_value docref_root 0 php_value docref_ext 0