댓글 스킨을 수정하시면 가능합니다.

/wp-content/plugins/kboard-comments/skin/default/list.php 파일을 수정해주세요.

아래 굵게 표시된 코드를 지워주시면 됩니다.

<select name="kboard_comments_sort" onchange="jQuery('#kboard-comments-sort-form-<?php echo $content_uid?>').submit();">
    <option value="best"<?php if($commentList->getSorting() == 'best'):?> selected<?php endif?>><?php echo __('Best', 'kboard-comments')?></option>
    <option value="oldest"<?php if($commentList->getSorting() == 'oldest'):?> selected<?php endif?>><?php echo __('Oldest', 'kboard-comments')?></option>
    <option value="newest"<?php if($commentList->getSorting() == 'newest'):?> selected<?php endif?>><?php echo __('Newest', 'kboard-comments')?></option>
</select>