Using Me (VB.NET) keyword is it required or not?

Private theString As String

Private Sub Setup(ByVal theString As String)
   Me.theString = theString
End Sub

Public Class ExampleClass

  Private FirstName As String

  Public Sub ExampleMethod()
    Dim FirstName As String
    FirstName = "Stefan"
  End Sub

End Class

Public Class ExampleClass

  Private FirstName As String

  Public Sub ExampleMethod()
    Dim FirstName As String
    FirstName = "Stefan"
    Me.FirstName = "Carl Gustav"
  End Sub

End Class

Class Sample
       Private myString as String

       Public Property GetMyString As String
       Get
          ' Some code here which sets the string after reading value from the  database
       End Get
       Set
       End Set

       End Property
End Class