Edit in JSFiddle

$(function() {

    $('.pun .post .user').each(function() {
        $(this).html($(this).html().replace(/<span class="label/g, '<dd><div class="post_field"><span class="label'));
    });

    $('.post_field:contains("Capa de Post:")').each(function() {

        var cover = $(this).text().split(': ')[1];
       
        $(this).parents('.user').css({
            'background-image': 'url(' + cover + ')'
        });

        $(this).remove();
   
    });

});