poormanscron successfully but old logs r not cleared.

Type Date Message User Operations
cron 09/04/2007 - 06:41 Akismet cron completed at 06:41:57. smily
cron 09/04/2007 - 06:41 Akismet cron started at 06:41:57. smily
cron 09/04/2007 - 06:41 Cron run completed (via poormanscron) smily
user 09/04/2007 - 06:41 Session opened for smily. smily

this is the log page.. when i logged in, the poormanscron executed the cronjob.. but even now the logs of previous 5 days r still there.. i have set them to clear every 1 day.

i had selected the option "Discard access logs older than: 1 day"..

now i set the option of clearing the log in to : "1 hour" and run the cron manually i.e through: Logs-->Status report--> the link: You can run cron manually (admin/logs/status/run-cron). i ran the cron manually.. but the same 5 days log r still there. this is the log

Type Date Message User Operations
cron 09/04/2007 - 06:56 Akismet cron completed at 06:56:18. smily
cron 09/04/2007 - 06:56 Akismet cron started at 06:56:18. smily
cron 09/04/2007 - 06:56 Cron run completed. smily

this is the oldest log that is still there :(
user 08/30/2007 - 16:53 New user: smily ... Anonymous edit

thanks for taking ur valuable time in helping me out. can u do me a favor in telling me how to remove this log directly.. that is going to the file mamanger and edit/delete these log files. where do i start.. i am totally confused where am i going as no error messaages r thrown .. so i dont know where to start.

this the content of cron.php
do i need to enter any data here ??

<?php 

// $Id: cron.php,v 1.36 2006/08/09 07:42:55 dries Exp $

/**
 * @file
 * Handles incoming requests to fire off regularly-scheduled tasks (cron jobs).
 */

include_once './includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
drupal_cron_run();

and why is <?php not ended with ?> tag. do i need to add that?? what can be addedd here. previously i had added the #!/usr/local/bin/php4.cli as the first line of the script to enable the cron run using the control panel>>cron jobs option. now since i have installed the poormanscron module i removed that line. the cron runs without a hitch and does not dispaly any errors but the logs remain. now what do i need to change??