Find and Replace

Try this:

Private Sub Worksheet_Change(ByVal Target As Range)
Dim KeyCells As Range
Set KeyCells = Me.Range("A1:A10")
           If Not Application.Intersect(KeyCells, Target) Is Nothing Then
Application.Enableevents = false
           For Each MyCell In Range("A1:A10")
               MyCell.Value = Replace(MyCell.Value, ",", ".")
           Next MyCell
Application.Enableevents = true
           End If
End Sub