Edit in JSFiddle

$(document).ready(function() {
  // add class to table
  $("table").addClass("table table-striped sortable");

  // delete width
  $("td").attr({
    "width": ""
  });


  // change all <td> in :first <tr> to <th>

  $("table tr:first td").each(function() {
    $(this).replaceWith('<th>' + $(this).text() + '</th>');
  });

  $("<thead></thead>").prependTo("table").append($("table tr:first"));
});

<table>
  <tr>
    <td width="00">Dag</td>
    <td width="85">US Date</td>
    <td width="73">Uur</td>
    <td width="78">Waar</td>
    <td width="78">Meer info</td>
    <td width="126">Website</td>
  </tr>
  <tbody>
    <tr>
      <td width="100">17/09/2016</td>
      <td width="85">09/17/2016</td>
      <td width="73">15u</td>
      <td width="78">Bla</td>
      <td width="78">Bla</td>
      <td width="126"><a href="http://www.aldofieuw.comm">www.aldofieuw.com</a></td>
    </tr>
    <tr>
      <td width="100">19/09/2016</td>
      <td width="85">09/19/2016</td>
      <td width="73">17u</td>
      <td width="78">Bla ba</td>
      <td width="78">Olala</td>
      <td width="126"><a href="http://www.mosterdpot.be">www.mosterdpot.be</a></td>
    </tr>
    <tr>
      <td width="100">06/09/2016</td>
      <td width="85">09/06/2016</td>
      <td width="73">19u</td>
      <td width="78">Bla Bla</td>
      <td width="78">Lorem ipsum</td>
      <td width="126"></td>
    </tr>
  </tbody>
</table>