$(document).ready(function() {
  $("#thumbs img").click(
    function(){
      var oldbig_src = $("#images img:first").attr("src");
      var oldbig_class = $("#images img:first").attr("class");
      
      $("#images img:first").attr("src", $(this).attr("class"));
      $("#images a:first").attr("href", $(this).attr("class").replace("_th2",""));
      //$("#images img:first").attr("class", $(this).attr("src"));
      
      //$(this).attr("src", oldbig_class)
      //$(this).attr("class", oldbig_src)    
    });
});