If IsPostBack Then
            Dim path As String = Server.MapPath("~/data/")
            Dim fileOK As Boolean = False
            If FileUpload1.HasFile Then
                Dim fileExtension As String
                fileExtension = System.IO.Path. _
                    GetExtension(FileUpload1.FileName).ToLower()
                Dim allowedExtensions As String() = _
                    {".jpg", ".jpeg", ".png", ".pdf"}
                For i As Integer = 0 To allowedExtensions.Length - 1
                    If fileExtension = allowedExtensions(i) Then
                        fileOK = True
                    End If
                Next
                If fileOK Then
                    Try
                        FileUpload1.PostedFile.SaveAs(path & _
                             FileUpload1.FileName)
                        Label1.Text = "File uploaded!"
                    Catch ex As Exception
                        Label1.Text = "File could not be uploaded."
                    End Try
                Else
                    Label1.Text = "Cannot accept files of this type."
                End If
            End If
        End If

<system.web>
    <httpRuntime maxRequestLength="size in kb" />
  </system.web>

 <httpRuntime
      executionTimeout="720"
      maxRequestLength="1048576"
/>