Hi guys.. i can bind csv file to Gridview but how can i update it?

Below is my code to Bind csv file to Gridview.

HTML
<asp:GridView ID="GridView" runat="server" DataKeyNames="postcode">
</asp:GridView>

CODE BEHIND

        'Upload and save the file
        Dim csvPath As String = Server.MapPath("~/csv/") + "location.csv"

        'Create a DataTable.
        Dim DT As New DataTable()
        DT.Columns.Add("Postcode")
        DT.Columns.Add("City")
        DT.Columns.Add("State")
        'DT.Columns.AddRange(New DataColumn(2) {New DataColumn("POSTCODE", GetType(Integer)), New DataColumn("CITY", GetType(String)), New DataColumn("STATE", GetType(String))})

        'Read the contents of CSV file.
        Dim csvData As String = File.ReadAllText(csvPath)

        'Execute a loop over the rows.
        For Each row As String In csvData.Split(ControlChars.Lf)
            If Not String.IsNullOrEmpty(row) Then
                DT.Rows.Add()
                Dim i As Integer = 0
                'Execute a loop over the columns.
                For Each cell As String In row.Split(","c)
                    DT.Rows(DT.Rows.Count - 1)(i) = cell
                    i += 1
                Next
            End If
        Next

        'Bind the DataTable.
        Me.GridView.DataSource = DT
        Me.GridView.DataBind()