As an alternate to the instructions posted above, If you have ftp access to your site files, you could directly edit the language file.
IN:
/languages/english/generic.php
FIND (near the top):
$ubbt_lang['CHARSET'] = "utf-8";
REPLACE WITH:
$ubbt_lang['CHARSET'] = "ISO-8859-1";
If you have language files other than "english" which you actively use, repeat this with each one of those.
