Function RemoveCharacters(InString As String) As String
    Dim intLoopCounter As Integer
    Dim intStringLength As Integer
    Dim intASCIIVal As Integer
    intStringLength = Len(InString)
    InString = LCase(InString)
    For intLoopCounter = 1 To intStringLength
        intASCIIVal = Asc(Mid(InString, intLoopCounter, 1))
        If (intASCIIVal >= 97 And intASCIIVal <= 122) Or (intASCIIVal >= 48 And intASCIIVal <= 57) Then
            RemoveCharacters = RemoveCharacters + Mid(InString, intLoopCounter, 1)
        End If
    Next intLoopCounter
End Function

RemoveCharacters

Visual Basic