Find and Replace based on lookup table

Option Explicit

Sub replaceX()
    Dim s1 As Worksheet, s2 As Worksheet
    Dim i As Long, j As Long
    Dim lr As Long, lr2 As Long
    Set s1 = Sheets("Data_Sheet")
    Set s2 = Sheets("Lookup_Sheet")
    lr = s1.Range("A" & Rows.Count).End(xlUp).Row
    lr2 = s2.Range("A" & Rows.Count).End(xlUp).Row
    With s1
        For i = 2 To lr
            For j = 2 To lr2
                If .Range("A" & i) = s2.Range("A" & j) Then
                    .Range("A" & i) = s2.Range("B" & j)
                End If
            Next j
        Next i
    End With
End Sub