This is a simple text replacement example. It will also work on Binary files since I included the description on how to make it reusable from a form with 3 text boxes and how to read in a full binary or ascii file as a single string. Usage:

Private Sub cmdReplaceText_Click()
    'replaces all occurances of Text2 in Text1 with Text3
    Call ReplaceTextInTextBox(Text1, Text2, Text3)
End Sub
Private Sub cmdReplaceFile_Click()
    'replaces all occurances of "hello" with "goodbye" in c:\test.txt, and saves the new file as c:\test_replace.txt
    Call ReplaceInFile("c:\test.txt", "c:\test_replace.txt", "hello","goodbye")
End Sub

Place the code below in a module

Public Function ReplaceTextInTextBox(MyTextBox As Object,_
       TextOld As Object, TextNew As Object)
 'The object reference is made form the form
 'you use to call this module. 
 'Assumed you have a text1, text2 and text3 text box on your form
 'where 1 is used for the text you wish to replace text in
 '2 is the one containing text you are searching for
 '3 is the new text you wish to see entered in its place.
 'The replacement function being called

  Call ReplaceText(MyTextBox.Text, TextOld.Text, TextNew.Text)

'Replace textview and refresh your form

    MyTextBox.Text = ReturnValue
    MyTextBox.Refresh

End Function



Public Function ReplaceInFile(InputFile As String, _
    OutputFile As String, OldT As String, NewT As String) As String
    Dim Fnum As Integer ' get a FreeFile number
    Dim FileLength As Long 'Just in case its really big
    Dim TheString As String


'I open the file as binary to avoid some
'complications with reading in a full file.
'This just so I can skip some trouble shooting with
'some special characters in certain exe files.
'It might be that character you wish to replace.

    Fnum = FreeFile
    Open InputFile For Binary As #Fnum ' Open file.
    FileLength = LOF(Fnum) ' Get length of file.

	TheString = Input(FileLength, #Fnum)

    Close #Fnum ' Close file.

'OldT = Whatever text you send form a form or function to search for
'NewT = Whatever text you wish to replace OldT with

'Call the function to replace text

   Call ReplaceText(TheString, OldT, NewT)

'Now print the result to a new file
'so you dont overwrite your original

    Fnum = FreeFile
    Open OutputFile For Output As #Fnum ' Open file.
    Print #Fnum, ReturnValue ' the ReturnValue from the replacement
    Close #Fnum ' Close file.

End Function


Public Function ReplaceText(CleanThis As String, _
    OldText As String, _
    NewText As String)

'To get the len of the string
    Dim StrLn As Long

'To split the string
    Dim PartA As String, PartB As String

'If search string is found, get its start position
    Dim FoundP As Long
    Dim OldLn As Long
    On Error GoTo ErrHandle

'Set a value for the len of the old text to be replaced
    OldLn = Len(OldText)
    StrLn = Len(CleanThis)

'Loop through the string until all occurences are eliminated

    Do While InStr(1, CleanThis, OldText) <> 0
        FoundP = InStr(1, CleanThis, OldText)

'Get PartA of the string (before found occurance)
        PartA = Left(CleanThis, FoundP - 1)

'Get PartB of the string (after found occurance)
        PartB = Right(CleanThis, StrLn - FoundP - OldLn + 1)

'*NOTE ON THE ADDITION AND SUBTRACTION**
'******************************************************
'+ 1 to avoid a skip in adding found len and old len
'The previous line could also be written
'     
'PartB = Right(CleanThis, StrLn - (FoundP + OldLn - 1))
'******************************************************
'REBUILD THE STRING BEFORE NEXT LOOP
'This adds a space before and after NewText
'and trims out unneccessary spaces too!
        
        CleanThis = Trim(PartA) & " " & _
        Trim(NewText) & " " & _
        Trim(PartB)
        'GET NEW LEN BEFORE LOOPING
        StrLn = Len(CleanThis)
    Loop

    'Set result of the function
    ReplaceInString = CleanThis 


'Avoid error handling
    Exit Function
'Add your own error code hereafter
    ErrHandle:
    Select Case Err.Number
        Case Err.Number
        MsgBox "Your function executed with an error " & Err.Number _
            & vbCrLf & vbCrLf & Err.Description, vbExclamation, _
            "Error " & Err.Number
        Err.Clear
    End Select
Resume Next
End Function