How to overwrite file in database with ajax

Question

I'm trying to replace some file in my DB using ajax call. I can not understand how to pass data(file) from my tag into controller, maybe somebody can give me an advise...

 

My controller:

[HttpPost]
public JsonResult UpdateFile(int id, HttpPostedFileBase postedFile)
{
   byte[] bytes;
   using (BinaryReader br = new BinaryReader(postedFile.InputStream))
{
   bytes = br.ReadBytes(postedFile.ContentLength);
}
         using (FileDBEntities db = new FileDBEntities())
         {
               tblFile fupt = db.tblFiles.Where(x => x.id == id).FirstOrDefault();
               fupt.Name = Path.GetFileName(postedFile.FileName);
               fupt.ContentType = postedFile.ContentType;
               fupt.Data = bytes;
               db.SaveChanges();
               return Json(new { success = true }, JsonRequestBehavior.AllowGet);
      }
}

my JS:

function loadFileData() {
         $.ajax({
            type: "GET",
            url: "/File/FileIndex",
            dataType: "JSON",
            success: function (data) {
               $.each(data, function (i, val) {
               var trow = $('<tr/>');
               var trowb = $('<tr/>').data("id", val.id);
               trow.append('<td colspan="2">' + val.Name + " " + '</td>');
               trowb.append('<td><input style="width:250px;" type="file" id="choose" /></td><td><input type="button"                value="upload" id="upload" /></td>');
               tab.append(trow);
               tab.append(trowb);
            });
                  $("#showFiles").html(tab);
         },
            error: function () {
                  alert("Failed! Please try again.");
               }
         });
                  var tab = $('<table style="width:300px" border=1 class=MyTable></table>');
                  tab.on("click", "#upload", function (e) {
                  //$('#uploadStatus').html("ok");
                  var tr = $(this).closest("tr");
                  var id = tr.data("id");
                  var input = $('#choose').file;
                           $.ajax({
                           type: "POST",
                           url: "/File/UpdateFile",
                           dataType: "JSON",
                           data: {
                           id: id,
                           pospostedFile: input
                           },
                                 success: function (data) {
                                 $('#uploadStatus').html("ok");
                                 loadFileData();
                           },
                           error: function () {
                                    alert("Failed! Please try again.");
                           }
                     });
                  });
            }

Debbuger says me that I'm sending "null" as "postedFile". How can I take this value from input and feed it to my Controller?