Hi Ramakrishna,
Try something like below code.
<div>
<uc1:abc id="uc1" runat="server"></uc1:abc>
<uc2:xyz id="uc2" runat="server" visible="false"></uc2:xyz>
</div>
protected void JoinButtonClicked(object sender, EventArg e)
{
uc1.visible=false;
uc2.visible=true;
}