Downloading file with space in filename

.aspx
 

 <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False">
                        <Columns>
                            <asp:TemplateField ShowHeader="False">
                                <ItemTemplate>
                                    <asp:LinkButton ID="lnkdownload" runat="server" CausesValidation="false"
                                        CommandArgument='<%#Eval("File_names") %>' CommandName=""
                                        Font-Underline="False" onclick="lnkdownload_Click"                           Text="Download">     </asp:LinkButton>
                                </ItemTemplate>
                            </asp:TemplateField>
                        </Columns>
                    </asp:GridView>


 .cs


protected void lnkdownload_Click(object sender, EventArgs e)
    {
        Response.Clear();
        LinkButton l1 = (LinkButton)sender;
        string filenm = l1.CommandArgument;
        Response.ContentType = ContentType; /*"application / octet - stream" if pdf;*/
        Response.AddHeader("Content-Disposition", "attachment; filename=\"" + Path.GetFileName(filenm) + "\"");
        Response.Charset = "";
        Response.WriteFile(filenm);
        Response.End();
}