Hi,
I tried some code for your requirement.Try this
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script src="Scripts/jquery-1.4.1-vsdoc.js" type="text/javascript"></script>
<script src="Scripts/jquery-1.4.1.js" type="text/javascript"></script>
<script language ="javascript" >
function f1() {
document.getElementById("fileupload1").parentElement.innerHTML = "<input type =\"file\" id=\"fileupload1\" />";
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<div id="divid" runat="server">
<input type ="file" id="fileupload1" />
</div>
<input type ="button" value="change" onclick ="f1()" />
<asp:button id="Button1" runat="server" text="Button" onclientclick="f1()" onclick="Button1_Click" xmlns:asp="#unknown" />
</div>
</form>
</body>
</html>
I hope It can works for you also.
I searched alot but i don't find correct solution because.
If we change file type input tags it leads to some security breaches .
finally I tried this code .I hope you understood what I said
If you use Jquery Then you can check user uploaded files in server side.
All the Best