Hi ashish007,

Check this example. Now please take its reference and correct your code.

HTML

<asp:Button ID="btnFileUpload" Text="Select File" runat="server" OnClick="Upload" />
<asp:FileUpload ID="FileUpload1" runat="server" Style="display: none" />
<br />
<asp:TextBox runat="server" ID="txtImage" TextMode="MultiLine" Height="120px" Width="120px" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
    $(function () {
        var fileupload = $("#FileUpload1");
        var button = $("#btnFileUpload");
        button.click(function () {
            fileupload.click();
        });
        fileupload.change(function () {
            var fileName = $(this).val().split('\\')[$(this).val().split('\\').length - 1];
            filePath.html(fileName);
        });
    });
</script>

Code

C#

protected void Upload(object sender, EventArgs e)
{
    decimal size = Math.Round(((decimal)FileUpload1.PostedFile.ContentLength / (decimal)1024 / (decimal)1024), 2);
    if (size <= 5)
    {
        FileUpload1.SaveAs(Server.MapPath("~/") + System.IO.Path.GetFileName(FileUpload1.PostedFile.FileName));
        txtImage.Attributes.Add("style", "background-repeat: no-repeat; background-image:url('" + System.IO.Path.GetFileName(FileUpload1.PostedFile.FileName) + "')");
    }
}

VB.Net

Protected Sub Upload(ByVal sender As Object, ByVal e As EventArgs)
    Dim size As Decimal = Math.Round((CDec(FileUpload1.PostedFile.ContentLength) / CDec(1024) / CDec(1024)), 2)
    If size <= 5 Then
        FileUpload1.SaveAs(Server.MapPath("~/") & System.IO.Path.GetFileName(FileUpload1.PostedFile.FileName))
        txtImage.Attributes.Add("style", "background-repeat: no-repeat; background-image:url('" & System.IO.Path.GetFileName(FileUpload1.PostedFile.FileName) & "')")
    End If
End Sub

Screenshot