更新本地与数据库中的图片

图片是以路径+图片文件名保存在数据库中，

图片存储在本地文件夹中，直接更新数据库中的图片文件名没问题，

但是要怎么把更新图片前的那张图片从本地文件夹中删除呢

下面贴出代码：

protected void btnUpload_Click(object sender, EventArgs e)
    {
        if (Session["username"] != null)
        {
            string uname = Session["username"].ToString();

            if (FileUserPic.PostedFile.FileName != null)
            {
                //获取文件完整的路径及名称
                string fullname = FileUserPic.PostedFile.FileName.ToString();
                //取得文件扩展名
                string ExName = fullname.Substring(fullname.LastIndexOf(".")+1);
                if (ExName.ToLower() =="jpg" || ExName.ToLower() == "gif" || ExName.ToLower() == "bmp")
                {
                    //获取文件名
                    string picname = System.IO.Path.GetFileName(fullname);
                    string cmdupdate = "update [aspnet_Users] set UserPic=@pic where UserName='" + uname + "'";
                    SqlConnection conn = new SqlConnection(help.SqlLink());
                    SqlCommand comm = new SqlCommand(cmdupdate, conn);
                    SqlParameter paraPic = new SqlParameter();
                    comm.Parameters.Add("@pic", SqlDbType.VarChar).Value = picname;

                    try
                    {
                        conn.Open();
                        comm.ExecuteNonQuery();   //@"H:/Images1"
                        DelAllPic(HttpRuntime.AppDomainAppPath + @"/Admin_Blog/UserPic");
                        FileUserPic.PostedFile.SaveAs(HttpRuntime.AppDomainAppPath + @"/Admin_Blog/UserPic/" + picname);
                        Response.Write("<script language='javascript'>alert('记录更新成功');</script>");
                        BindUserPic();
                    }
                    catch { }
                    finally
                    {
                        conn.Close();
                    }
                }
                else
                {
                    Response.Write("<script language='javascript'>alert('请重新选择上传图片格式');</script>");
                }
            }
            else
            {
                Response.Write("登录超时或者用户名为空，请重新登录");
            }
        }
    }