Mass Changing Of Options For ALL Users

You have two options:

install phpMyAdmin and enter that text into the query box and run it

OR

create a new file called something.php and enter the following code into it:

PHP Code:

<?php
include "global.php";

$result = $DB_site->query("UPDATE user SET receivepm=1");

echo "successfully executed query";
?>

Now copy that file into the same folder as your forums and visit it once with a web browser. If the page returns 'successfully executed query' then you have just altered every user's profile.

Then delete the something.php file.