Replacing Numbers from One Sheet to Another

Assuming the lookup list in Sheet2 starts from A1:B1 down.
The numbers to be replaced are in Sheet1.

Sub test()
    Dim r As Range
    For Each r In Sheets("sheet2").Range("a1").CurrentRegion.Columns(1).Cells
        Sheets("sheet1").Cells.Replace r.Value, r(, 2).Value, 1
    Next
End Sub