Here I have created sample that will help you out.
HTML
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript">
$(function () {
$('[id*=txtName]').hide();
$('[id*=lblName]').click(function () {
$(this).hide();
$('[id*=txtName]').val($(this).html().trim());
$('[id*=txtName]').show();
});
});
</script>
</head>
<body>
<div>
Name:
<label id="lblName">
AspSnippets
</label>
<input type="text" id="txtName" />
</div>
</body>
</html>
Demo
Same you can achive using asp.net controls,use the same script and below controls.
<asp:Label ID="lblName" Text="AspSnippets" runat="server" /><asp:TextBox ID="txtName"
runat="server" />
