how to replace a word in specific line in text file

It is guessing, but this changes faux in the second line

        Dim TheLines = Split(TextBox1.Text, Environment.NewLine)
        TheLines(1) = TheLines(1).Replace("faux", "OK") 'changes the second (2) line'
        TextBox1.Text = String.Join(Environment.NewLine, TheLines)

Success
Cor