The simplest approach is to rename File B as File A.
Or you could use a macro like:
Code:
Sub ChangeLinks()
Dim Sld As Slide, Shp As Shape
For Each Sld In ActivePresentation.Slides
For Each Shp In Sld.Shapes
With Shp
If .Type = 10 Then
With .LinkFormat
.SourceFullName = Replace(.SourceFullName, "File A.xlsx", "File B.xlsx")
.Update
End With
End If
End With
Next
Next
End Sub