If you put a phpinfo.php file in your webroot for Magento, a simple file with just the line:
<?php phpinfo() ?>
Then open the file in your browser, then how much memory does it say?
Restart httpd and it will probably be the same.
If I were you I would make the change in php.ini, usually /etc/php.ini, but it could be different - see what your phpinfo says…
After changing php.ini service restart httpd to get it read in again.