Working Macro not auto updating

Hello All, and thanks for any feedback. This is in Excel 2013

I have the following Macro in my workbook which does exactly what it is suppose to do when I run the macro,
but it does not run on it's own like it suppose to do??? What did I do wrong here?

Sub Worksheet_Change()
Application.ScreenUpdating = False
    ActiveWorkbook.Worksheets("Clients").Sort.SortFields.Clear
    ActiveWorkbook.Worksheets("Clients").Sort.SortFields.Add Key:=Range("L2:L100" _
        ), SortOn:=xlSortOnValues, Order:=xlAscending, CustomOrder:="YES,NO", _
        DataOption:=xlSortNormal
    ActiveWorkbook.Worksheets("Clients").Sort.SortFields.Add Key:=Range("C2:C100" _
        ), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal
    With ActiveWorkbook.Worksheets("Clients").Sort
        .SetRange Range("A1:L100")
        .Header = xlYes
        .MatchCase = False
        .Orientation = xlTopToBottom
        .SortMethod = xlPinYin
        .Apply
    End With
    Application.ScreenUpdating = True
End Sub

Thanks for any input

Declaration is not correct - it must be:

Private Sub Worksheet_Change(ByVal Target As Range)

Also code must be in module for correct worksheet.

Also:

Did you put the code in the Clients worksheet's code module and not in a standard code module like Module1?

Do you want it to run on any change to the worksheet?

As Izandol pointed out, it has to be called exactly this...

Private Sub Worksheet_Change(ByVal Target As Range)

And it's only located in the worksheet code module. Not in Module1.

EDIT: disregard