Try:
Code:
Sub ChangeColumnFontSize()
'Change the Font Size in Selected columns in all tables
Application.ScreenUpdating = False
Dim Tbl As Table, i As Long
For Each Tbl In ActiveDocument.Tables
With Tbl.Columns(1)
For i = 1 To .Cells.Count
.Cells(i).Range.Font.Size = 14
Next
End With
With Tbl.Columns(3)
For i = 1 To .Cells.Count
.Cells(i).Range.Font.Size = 14
Next
End With
Next
Application.ScreenUpdating = True
End Sub