Try below code to enter upper case value, just copy and paste in coding area of particular sheet.
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim Rng, R As Range
Dim i, j As Integer
Set Rng = Range("A1:A100") 'Change range as per requirement
If Not (Application.Intersect(Target, Rng) Is Nothing) Then
For Each R In Rng
For i = 1 To Len(R)
For j = 97 To 121
If Mid(R, i, 1) = Chr(j) Then
'Remove inverted comma (') from below two line to clear lower case value from cell range.
'MsgBox "Lowe case not allowed in cell " & R.Address, vbOKOnly
'R.Clear
R = UCase(R) 'Transfer to Upper case in cell Range
End If
Next j
Next i
Next R
End If
End Sub
Regards
Ashish Bhalara