how change the image in adrotator

Question

i want every twenty second change the image in adrotator
i used scriptmanager and timer controlUpdatePanel,Triggers,ContentTemplate,AdRotator then add advertisement file :add of xml file .this controls change the image every seconds .please help me
my code behind sourse is given below
<form id="form1" runat="server">
    <div>
        <asp:ScriptManager ID="ScriptManager1" runat="server">
        </asp:ScriptManager>
    </div>
        <asp:Timer ID="Timer1" runat="server" OnTick="Timer1_Tick" Interval="1000">
        </asp:Timer>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <Triggers>
        <asp:AsyncPostBackTrigger ControlID="Timer1" EventName="Tick" />
        </Triggers>
            <ContentTemplate>
                <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
                <asp:AdRotator ID="AdRotator1" runat="server"  style="z-index: 103; left: 450px; position: absolute; top: 57px"  />
                 <asp:TextBox ID="TextBox1" runat="server" style="z-index: 100; left: 283px; position: absolute; top: 143px"></asp:TextBox>
            </ContentTemplate>
        </asp:UpdatePanel>
    </form>