jQuery addClass example
Change class name on click in jQuery
HTML
<table id='table'>
<tr>
<td class='td-class'>ex</td>
<td>ex2</td>
</tr>
</table>
JavaScript
$('#table').on('click','td.td-class', function (e) {
$(this).html('<select><option value="volvo">Volvo</option><option value="saab">Saab</option><option value="mercedes">Mercedes</option><option value="audi">Audi</option></select>');
});