I'm not sure on what exactly you are expecting so all we can do is simplify what your code is already doing to make it more straightforward. This won't work any differently to what you already had.
Code:
Sub Macro1()
With Selection.Find
.Wrap = wdFindContinue
.Text = ChrW(257)
.Replacement.Text = "A"
.Execute Replace:=wdReplaceAll
.Text = ChrW(275)
.Replacement.Text = "E"
.Execute Replace:=wdReplaceAll
.Text = ChrW(299)
.Replacement.Text = "I"
.Execute Replace:=wdReplaceAll
.Text = ChrW(333)
.Replacement.Text = "O"
.Execute Replace:=wdReplaceAll
.Text = ChrW(363)
.Replacement.Text = "U"
.Execute Replace:=wdReplaceAll
End With
End Sub