My Link Order doesn’t work

I get the following error whenever I try to access “My Link Order”:

The file /home/httpd/vhosts/aquilah.com/httpdocs/wp-includes/taxonomy.php is not writable.
You have 2 options:
1. Change the permissions on the file and click on My Link Order again to patch it automatically.
2. Modify the file manually :
After line number 619 :
$orderby = ‘t.term_group’;
add the following code:
else if ( ‘order’ == $orderby )
$orderby = ‘t.term_order’;

How do I fix this? Call me dumb, but I don’t see where I can change the permissions. And , $orderby = ‘t.term_group’; shows up two times in the code, and it’s not numbered to know which is which. Any help is appreciated. Thanks!