If you have root access, log on to your server as root and do the followings:
[root@lazybox ~]# cd /usr/local/apache/logs/[root@lazybox logs]# lsaccess_log error_log httpd.pid suphp_log[root@lazybox logs]# >access_log[root@lazybox logs]# >error_log[root@lazybox logs]# >suphp_log[root@lazybox logs]#
Basically, command >filename removes all contents of a file.