how is iframe visibility change in buttion click event? in asp.net

how is iframe visibility change in buttion click event? in asp.net
<td valign="middle" style="width: 270px;">
<asp:UpdatePanel runat="server" ID="pan">
<ContentTemplate>
<asp:ListBox ID="lstContact" Width="503px" runat="server"></asp:ListBox>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="imgbrowse" EventName="Click" />
<asp:AsyncPostBackTrigger ControlID="imgifrmremove" EventName="Click" />
</Triggers>
</asp:UpdatePanel>
</td>
<td style="border-left: none" valign="bottom">
<div>
 <asp:ImageButton ID="imgifrmremove" AlternateText="To Address" runat="server" />
<br />
 <asp:ImageButton ID="imgbrowse" AlternateText="To Address" runat="server" />
<br />
 <asp:ImageButton ID="imgemailremove" AlternateText="Remove Email ID" runat="server" />
</div>
</td>
</tr>
<tr class="Rowstyle" >
<td colspan="3" runat="server" id="frm">

<div>
<iframe src="ConLecture.aspx" width="100%" height="500px" visible="true" id="conlect" runat="server">
</iframe>
</div>

</td>





Protected Sub imgifrmremove_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles imgifrmremove.Click
imgifrmremove.Visible = True
imgbrowse.Visible = False
End Sub

Protected Sub imgbrowse_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles imgbrowse.Click
imgifrmremove.Visible = False
imgbrowse.Visible = True
End Sub

but this is not worked .please help me
Thanks for Advance