File.delete(path);
或
FileInfo  fi=new FileInfo(path);
fi.delete();

File.Delete(path);
或
FileInfo  fi=new FileInfo(path);
fi.Delete();

            Database db = new Database();
            DataRow dr = db.GetDataRow("select top 1 l_logo from link where     l_id="+Request.QueryString["id"]);
            System.IO.File.Delete(Server.MapPath(dr["l_logo"].ToString()));