removeClass & addClass not working

removeClass & addClass not working

remove & addClass functions do not work. I am trying trying to make sure that the span class changes to a new one once it is clicked.

here's the jquery code:
  1.     $('.vote_btn').click(function(){
          $.ajax({
            url:'/joseph/pages/votes.php',
            type: 'post',
            //dataType:'json',
            data:{'comment_id':$(this).data('commentid')},
            success: function(data){
              if(data == 'up'){
                  $(this).removeClass('fa-thumbs-o-up').addClass('fa-thumbs-up');
              } else if(data == 'reversed') {
                  $(this).removeClass('fa-thumbs-up').addClass('fa-thumbs-o-up');
              } else {
                alert(data);
              }
            }
          });
        });
      });


and here is the HTML code:

  1. <span id="<?=$comment['id']?>" class="fa fa-thumbs-o-up vote_btn"></span>