function cambiaParam(id,param) {
  var url=''
  var objURL = new Object()
  window.location.search.replace(new RegExp("([^?=&]+)(=([^&]*))?", "g" ),function( $0, $1, $2, $3 ){
     objURL[$1] = $3;
  })
  var params="";
  var cont=0;
  var apar=0;
  for (var strKey in objURL) 
  {
    var separ=(cont++==0) ? "?" : "&";
    var parametro="";
    if (strKey==param) {
        parametro= param+"="+id;
        apar++;
    }
    else parametro = strKey+"="+objURL[strKey];
    params+=separ+parametro;     
  }
  if ((apar==0) && (cont>0)) params+="&"+param+"="+id;
  if (cont==0) params="?"+param+"="+id;
  var p=window.location.href.split('?');
  window.location.href=p[0]+params;
}