convert existing code to asynchronous workings - asp.net

Question

I have existing code in VB in which I need to process all records that are in the list in one go, and await for their responses. When they respond, add them to the data table. The code works. I just need to convert it to run asynchronously.
Here is my code:
Imports System.Net
Imports System.IO
Public Class Form1
Dim _Datatable As New DataTable
Private Sub btnProcess_Click(sender As System.Object, e As System.EventArgs) Handles btnProcess.Click
prgProgress.Value = 0
prgProgress.Maximum = lstUrls.Items.Count
For Each _ProductEntry As String In lstUrls.Items
Try
Dim _Webclient As New WebClient
'_Webclient.Proxy = _ProxyClient
Dim _DataStream As Stream = _Webclient.OpenRead(New Uri(_ProductEntry))
Dim _DataRead As New StreamReader(_DataStream)
Dim _HtmlContent As String = _DataRead.ReadToEnd
Dim _HtmlDocument As mshtml.IHTMLDocument2 = New mshtml.HTMLDocument
_HtmlDocument.write(_HtmlContent)
Dim _ProductName As mshtml.IHTMLHeaderElement = _HtmlDocument.getElementById("product-header")
_DataStream.Close()
_DataRead.Close()
Call CheckTable("Name")
Call CheckTable("URL")
Call CheckTable("Image")
Call CheckTable("Price")
Dim _Price As String = String.Empty
Dim _SpanElements As mshtml.IHTMLElementCollection = _HtmlDocument.getElementsByTagName("span")
For Each _SpanElement As mshtml.IHTMLSpanElement In _SpanElements
If _SpanElement.classname = "regular-price" Then
_Price = Replace(Replace(_SpanElement.innertext, "£", ""), "Incl. VAT", "")
End If
Next
Dim _ImageLocation As String = String.Empty
For Each _Paragraph As mshtml.IHTMLElement In _HtmlDocument.getElementsByTagName("image")
If _Paragraph.id = "product-image-main" Then
Dim _Image As mshtml.IHTMLImgElement = CType(_Paragraph, mshtml.IHTMLImgElement)
_ImageLocation = _Image.src
Exit For
End If
Next
Dim tableElements As mshtml.IHTMLElementCollection
tableElements = _HtmlDocument.getElementsByTagName("Table")
Dim oTableTest As mshtml.IHTMLTable2 = tableElements.item(1)
'BUILD HEADERS
For Each _ColumnHeader As mshtml.IHTMLTableRow In oTableTest.rows
CheckTable(CType(_ColumnHeader.cells(0), mshtml.IHTMLElement).innerText)
Next
Dim _DataRow As DataRow = _DataTable.NewRow
_DataRow.Item("Name") = CType(_ProductName, mshtml.IHTMLElement).innerText
_DataRow.Item("URL") = _ProductEntry
_DataRow.Item("Price") = _Price
_DataRow.Item("Image") = _ImageLocation
For Each _RowData As mshtml.IHTMLTableRow In oTableTest.rows
Dim _Header As mshtml.IHTMLElement = _RowData.cells(0)
Dim _Value As mshtml.IHTMLElement = _RowData.cells(1)
_DataRow.Item(_Header.innerText) = _Value.innerText
Next
Dim _Elements As mshtml.IHTMLElementCollection = _HtmlDocument.all
For Each _Element As mshtml.IHTMLElement In _Elements
If _Element.className = "product-description product-documents" Then
For Each _ProductLink As mshtml.IHTMLElement In _Element.all
If _ProductLink.tagName = "A" Then
CheckTable(_ProductLink.innerText)
_DataRow(_ProductLink.innerText) = Replace(CType(_ProductLink, mshtml.IHTMLAnchorElement).href, "about:", "http://www.tapoutlet.co.uk")
End If
Next
End If
Next
_DataTable.Rows.Add(_DataRow)
_DataTable.AcceptChanges()
dgvScrapedData.DataSource = _Datatable
dgvScrapedData.Refresh()
Catch ex As Exception
Console.WriteLine("Error getting webpage-" & _ProductEntry)
Console.WriteLine(ex.Message.ToString)
End Try
Next
End Sub
Private Function CheckTable(ByVal ColumnName As String) As Boolean
If _DataTable.Columns.Contains(ColumnName) Then
Return True
Else
_DataTable.Columns.Add(ColumnName)
Return False
End If
End Function
End Class