You probably can't delete or modify the old post after this long, there's usually an expiry date on this sort of action. As previously mentioned, the best way to contact the administrators and ask them to delete the post.
The other solution is that you can reply to your own post and retract your initial comments if you no longer support them. Sometimes openly reversing and correcting your statements is more useful than trying to retract them.
I imagine the problem you're having wouldn't actually be a problem if the individual involved had of simply done their best to fix the problem, rather than wishing it away.