User Confirmation before Deleting Items in ASP.Net 2.0

Attach the OnClientClick event to the button as below

asp:button id="btnapprove" tabindex="65" runat="server" cssclass="buttonstyle" text="Update Status" onclientclick="return confirm('Are you sure you want to delete this Contact Record?');"

JavaScript for Filter Action in FileUpload Control

function Trim(input)
{
var lre = /^\s*/;
var rre = /\s*$/;
input = input.replace(lre, "");
input = input.replace(rre, "");
return input;
}
function CheckForImageFile()
{
var file = document.getElementById('<%=uploadLogo.ClientID%>');
var fileName=file.value;
var extArray = new Array(".jpg", ".JPG", ".gif", ".GIF", ".png", ".PNG",
".bmp", ".BMP", ".jpeg", ".JPEG","");
while (fileName.indexOf("\\") != -1)
fileName = fileName.slice(fileName.indexOf("\\") + 1);
var ext = fileName.slice(fileName.indexOf(".")).toLowerCase();
for (var i = 0; i < extArray.length; i++)
{
if (extArray[i] == ext)
{
return true;
}
}
alert("Please only upload images that end in types: "
+ (extArray.join(" ")) + "\nPlease select a new "
+ "image to upload and submit again.");
file.focus();
return false;
}