Open the ACE program, select the specific aircraft (model and livery), and checkmark (place a tick in) the box next to Winglets, then click on Save Changes (see attached image).

Open the aircraft.cfg using Notepad, then edit the ui_wglts=0 to ui_wglts=1 like this:

[fltsim.0]
title=Captain Sim 757-200 FSX 0
sim=cs757-200
model=PW
panel=
sound=PW
texture=delta
kb_checklists=
kb_reference=
atc_id=N675DL
atc_airline=Delta
atc_flight_number=757
ui_manufacturer=Boeing
ui_type=757-200 PW
ui_variation=Delta
ui_typerole="Commercial Airliner"
ui_createdby="Captain Sim"
description=757 Captain (757-200 Base Pack) v.4.6\n(c) 2011 Captain Sim \nwww.captainsim.com
ui_wglts=0 <- change this to ui_wglts=1

An easy way to do all of them in one hit, is to press CTRL+H, add ui_wglts=0 to the Find what: field, then add ui_wglts=1 in the Replace with: field, then click on Replace all.

You can click on Find next, then click on Replace to only change the ones you want changed. If you prefer that.

Backup the aircraft.cfg BEFORE making any changes!!!

Note. Don't worry about the Replace all replacing something in the wrong place, as it won't. All your 757 will (or at least should) have winglets visible on them.

the ui_wglts=0
is not in my cfg

ok thx