Don't need variables in his case.

FullSeriescollection was introduced in 2013. It's is slightly different (having to do with filtered data) than the usual .SeriesCollection but probably is irrelevant in this case. Use Seriescollection for backward compatibility.

Sub editseriescollection()
    With ActiveSheet.ChartObjects("Gráfico 1").Chart
        .SeriesCollection(2).Values = "=qry_123!C2:C" & Range("qry_123!C2").End(xlDown).Row
        With .SeriesCollection(2).Format.Fill
            .Visible = msoTrue
            .ForeColor.RGB = RGB(0, 112, 192)
            .Transparency = 0
            .Solid
        End With
        .SeriesCollection(1).XValues = "=qry_123!E2:E" & Range("qry_123!E2").End(xlDown).Row
        .SeriesCollection(1).Format.Fill.Visible = msoFalse
    End With
End Sub