Webforms: Is it possible to set a delete field button?
This link seems to have some solution. Clear upload file input field with jQuery

The relevant js is given below. 


  The HTML of any element can be reset with jQuery using the following
  function and passing in the id of the element's parent. This will
  reset the HTML within the parent to its original state; it will lose
  any binding you'd added after the DOM was loaded (such as adding an
  event handler in $(document).ready). Here's the Javascript for doing
  this:


function reset_html(id) {
    $('#'+id).html($('#'+id).html());
}



  In $(document).ready we can now add a div around every  element with a clear button, binding a function to it
  which will reset the HTML of the div like so:


$(document).ready(function() {

    var file_input_index = 0;
    $('input[type=file]').each(function() {
        file_input_index++;
        $(this).wrap('&lt;div id="file_input_container_'+file_input_index+'"&gt;&lt;/div&gt;');
        $(this).after('&lt;input type="button" value="Clear" onclick="reset_html(\'file_input_container_'+file_input_index+'\')" /&gt;');
    });

});


Note : I have not tested this out myself.