Web Forms :: How To Get Changed Data In C# After Changing Data Using Javascript

I sort a listbox items, using code below:

<script type="text/javascript">
function MoveDown() {
var selectedOption = $('#ListBox1 > option[selected]');
var nextOption = $('#ListBox1 > option[selected]').next("option");
if ($(nextOption).text() != "") {
$(selectedOption).remove();
$(nextOption).after($(selectedOption));
}
}
function MoveUp() {
var selectedOption = $('#ListBox1 > option[selected]');
var prevOption = $('#ListBox1 > option[selected]').prev("option");
if ($(prevOption).text() != "") {
$(selectedOption).remove();
$(prevOption).before($(selectedOption));
}
}
</script>

But when I submit a button and get listbox item in c#, I just get the order which not changed. How to get the changed data?