<form id="form1" runat="server">
    <div>
        <asp:ScriptManager ID="ScriptManager1" runat="server" />
    </div>
    <asp:LinkButton ID="LinkButton1" runat="server" onclick="LinkButton1_Click">LinkButton</asp:LinkButton>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server" Visible="False">
        <ContentTemplate>
            <asp:Label ID="Label1" runat="server" Text="BAMBA" Font-Size="XX-Large"></asp:Label>
        </ContentTemplate>
        <Triggers>
        <asp:AsyncPostBackTrigger ControlID="LinkButton1" EventName="Click"/>
        </Triggers>
    </asp:UpdatePanel>
    </form>

 protected void LinkButton1_Click(object sender, EventArgs e)
    {
        bool visible = UpdatePanel1.Visible;
        
        if(visible)
        {
            UpdatePanel1.Visible = false;    
        }
        else
        {
            UpdatePanel1.Visible = true;
        }
        
    }

 <Triggers>
                    <asp:AsyncPostBackTrigger ControlID="lnkChangePWD" EventName="Click" />
                    </Triggers>