Setting PHP permissions

Forgive me if this is incredibly stupid, but I’m trying to install the phpBB forum and am stuck on the second step! Their install guide says to “Change the permissions on config.php to be writeable by all (666 or -rw-rw-rw- within your FTP Client)”. HOW? Did I download it wrong, because that file comes up blank (as in zero K) in both my FTP client (Transmit) and my web browser (Safari and IE). Thanks so much to the person who can clear this up.