To view utility-functions.php, you will need to either go through the FTP since the default wordpress editor is quite limited in function and does not go deeper than 1 level or so when looking for files part of the theme. If you do want to get to it from the wordpress admin, pls install the following plugin named Synchi –
I use it all the time for support since the default editor does not help much. If you still have an issue, pls post a private message with the login and I can make the change.
One more thing, it is safer to make PHP code changes from FTP since a single error can bring down the site with no access to WP admin console or the above plugin. It is easy to revert back to original code if that happens if you are on FTP. Pls have a backup to restore back.