How Do I Fill File Stream

FileStream stream = new FileStream("c:\aaa.jpg",FileMode.OpenOrCreate);

string fileName = Path.GetFileName(File_Upload.PostedFile.FileName);
        string path = (ConfigurationManager.AppSettings["virtual_path"]).ToLower();

        Btn_upload.Enabled = false;
        File_Upload.Enabled = false;

        try
        {
            con.Open();
            SqlCommand cmdInsert = new SqlCommand("insert into tbl_Img (Fld_Uploader,Fld_path,Fld_mode) values ('admin','" + path + "','aaa')", con);
            cmdInsert.ExecuteNonQuery();

            SqlCommand cmdSelect = new SqlCommand("select top 1 * from tbl_Img order by Fld_id desc ", con);
            SqlDataAdapter da = new SqlDataAdapter(cmdSelect);
            DataTable dt = new DataTable();

            da.Fill(dt);
            
            ImgId = dt.Rows[0]["Fld_id"].ToString();
            RandCode = dt.Rows[0]["Fld_RandCode"].ToString();
            ImgName = ImgId + "_" + fileName;

            path = path + ImgId + "_" + fileName;

            string aaa = Server.MapPath("~/" + path);


            FileStream stream = new FileStream(aaa,FileMode.OpenOrCreate);

           // StreamWriter str = new StreamWriter(aaa);
            Response.Write(aaa);

            stream.Close();
            //File_Upload.PostedFile.SaveAs(Server.MapPath(stream.ToString()));

            SqlCommand cmdUpdate = new SqlCommand("update tbl_Img set Fld_FileName = '" + ImgId + "_" + fileName + "' where Fld_id = '" + ImgId + "' ", con);
            cmdUpdate.ExecuteNonQuery();


            con.Close();

            Img.ImageUrl = "../../ReadAttachment.aspx?code=" + RandCode + "&maxWidth=100&maxHeight=100";
        }
        catch (Exception ex) 
        {
            ErrorDiv.Attributes["class"]="ErrorDivVisible";
            array[count++] = "مشکلی در آپلود فایل وجود دارد";
            array[count++] = ex.Message;
            flag = 1;
            UlFunction(count, array);
        }

        BtnDelete.Visible = true;
        btnAdd.Enabled = true;
    }