Tienes que utilizar un StreamReader para leer el fichero. Luego utiliza la función replace de VB.
Para leer el fichero ....
Imports System.IO
Dim sr As StreamReader = New StreamReader("TestFile.txt")
Dim line As String
' Read and display the lines from the file until the end
' of the file is reached.
Do
line = sr.ReadLine()
Console.WriteLine(Line)
Loop Until line Is Nothing
sr.Close()
Para usar Replace ...
Dim correctString As String = errString.Replace("@@LINK@@)", "Nuevo texto!")
Saludos,
DJK