Hi, I tried to create a small demo on this problem. This might be helpful to you.
<script type="text/javascript">
$(document).ready(function () {
var counter = 2;
function addRow() {
var html = '<tr class="rowstyle"><td>Select File: <input type="file" id="FU' + counter + '" name="FU' + counter + '"></td><td><input type="button" class="BtnPlus" value="+" /></td><td><input type="button" class="BtnMinus" value="-" /></td>'
$(html).appendTo($("#MAndP1"))
counter++;
};
$("#MAndP1").on("click",".BtnPlus", addRow);
});
</script>
<table id="MAndP1" cellspacing="3">
<tr class="rowstyle">
<td>Select File: <asp:FileUpload ID="FU1" runat="server" /></td>
<td><input type="button" class="BtnPlus" value="+" /></td>
<td><input type="button" class="BtnMinus" value="-" /></td>
</tr>
</table>