I'm assuming your running a unix machine with apache since you didn't say, and I have to make this assumption so I don't go nuts.
If you have root access on that machine, then you can "chown webuser.webgroup filename" Where webuser and webgroup is what apache is run as, sometimes called nobody, sometimes it's called 'http', sometimes something else.
If you don't have root on the server, then you can "chmod 666 filename" but this is insecure, as now all users on the machine will be able to access this file, actually the other method is insecure also as any users that can write php code can access it, but what are you gonna do?