Replace any letter [A-Z] in a range with vba - excel

Question

I have a free text field that contains both text and numbers of varying lengths. I need to replace any letter in the column with "x". I have had success with replacing specific text using 'rng.replace' but need to include any letter [A-Z]
Dim rng as Range, lastRow As Long
lastRow = ActiveSheet.Range("A" & Rows.Count).Emd(xlUp).Row
Set rng = ActiveSheet.Range("E2:E" & lastRow)
rng.replace What:=[A-Z], Replacement:="x", MatchCase:=False
I cannot get the correct syntax for "What" to match any and all letters A-Z
Any help would be appreciated. I have a loop that works, however, it is very slow and stalling my overall process too much. I have worked the above rng.replace into speeding up the process for everything except this "text" replace.

Answer 1

Plenty of ways to skin a cat it seems.
Dim Number As Long
Dim Letter As String
Set Rng = Range("A1")
For Number = 1 To 28
Letter = Split(Cells(1, Number).Address, "$")(1)
Rng.Replace What:=(Letter), Replacement:="x", MatchCase:=False
Number = Range(Letter & 1).Column
Next

Answer 2

If performance is an issue, it's usually faster to do this by checking the byte values of the string array. Something like this:
Public Function ReplaceAlphas(txt As String) As String
Dim i As Long, a As Long
Dim b() As Byte
b = txt
For i = 0 To UBound(b) Step 2
a = b(i)
If (a >= 65 And a <= 90) Or (a >= 97 And a <= 122) Then
b(i) = 120
End If
Next
ReplaceAlphas = b
End Function

Answer 3

Try the next function, please:
Function removeLetters(strX As String) As String
With CreateObject("vbscript.regexp")
.Pattern = "[^0-9]" 'pattern to replace everything except numbers
.Global = True
removeLetters = .Replace(strX, "X")
End With
End Function
To use it for a range, please try the next code:
Sub testRngRemoveLetters()
Dim sh As Worksheet, rng As Range, C As Range, usedCol As Long, lastRow As Long
Set sh = ActiveSheet ' use here your sheet
usedCol = 2 'column B:B. Use the column number you need
lastRow = sh.cells(Rows.count, usedCol).End(xlUp).Row 'last row on the chosen column
'building the range to be processed:
Set rng = sh.Range(sh.cells(2, usedCol), sh.cells(lastRow, usedCol))
'Use the above function to replace everything else then numbers:
For Each C In rng
C.value = removeLetters(C.value)
Next
End Sub
Please, test it and send some feedback...