The value for meta_order in qa-lang/qa-lang-main.php just specifies the default order. The implementation of which elements appear in which order is actually in the method post_meta() in qa-include/qa-theme-base.php. You can change it by overriding the method in your theme (in qa-theme.php to be precise).
Add something like this to your theme:
class qa_html_theme extends qa_html_theme_base {
...
function post_meta($post, $class, $prefix = null, $separator = '<br/>') {
...
$order = Array('where', 'who', 'when', 'what');
foreach ($order as $element) {
...
}
...
}
...
}
Changing core files is not recommended, as the changes will be lost when updating Q2A.