Replacing 3 bulb fixture with LED fixture
Stop. The wires coming from the ceiling must be left as they are
For some reason, this one drives people crazy.  If a lamp takes multiple wires, and people see multiple wires coming from the ceiling to the fixture, they think there's some sort of correspondence.  There's not.

Example: If you see 3 white wires coming from the ceiling, and 3 white wires going to the 3 bulbs in the fixture, and they're all clumped together, they are so for a reason.  The 3 white wires are not only communicating with the 3 lamp bulbs, but also with each other.
the fact that it's 3 and 3 is pure coincidence. The ceiling-3’s first job is to connect the three ceiling wires with each other.  Because those wires have other jobs unrelated to this light. Their second job is to provide the necessary service to the light-3.

So people take apart the wires from the ceiling because they think the ceiling wires are all about the light. After they discover this is wrong, they have the wires all confused and are unable to put them back the way they were.  We see this all the time, we had one just yesterday.
Here's what you do
Take photos.  Notice that all the black wires from all the lamps goes to one single wire nut.  There will be one or more other wires from the ceiling also going into that nut. Whatever you do, those wires from the ceiling need to remain connected to each other.
The same applies to the lamp white wires.
The ceiling wires could be any conceivable color, and may also be the same color as other wires going into other wire nuts.  If that offends your OCD, more on that later. Color coding is simply not a thing.  The colors are a side-effect of cable manufacture, they must be made different so they can be distinguished on the other end.  Real electricians rely on testing, position and grouping to determine which wires are which.
Although in all probability, the white-wire group will be all-white.  Don't get too excited about that, it's a special rule for neutrals -neutrals must be white, but white wires are not necessarily neutral.
You may also find other groups of wires nutted together that do not connect to the lamp.  Leave those alone. Seriously.
So all the white wires from the new fixture goes into the same bundle of wires that all the white wires from the old fixture went to, and all the other wires in that bundle stay together.
Ditto black.
If you were simply removing the fixture, then the new fixture would have 0 wires obviously, but the bundle of wires in the ceiling that was together before, must still be together. If removing the lamp wire(s)  leaves a ceiling wire solo, it is capped. Do not split groups.
With safety grounds, follow the lead of the last fixture. Grounds are always green, yellow/green or bare, except in the old Soviet Bloc.  It is the only color code that is reliable.
Marking wires by function
I can't stand seeing 3 black wires in a box each doing different jobs.  That's why I own 10 colors of electrical tape.  (5 will do). That is why I wrap tape around wires to re-mark wires by their function:

black for always-hot (you use that in switch loops)
red for switched-hot (this wire invariably feeds a lamp, note that the wires on lamps themselves are black)
white for neutral, but you don't have a choice here, since every cable has white, and if neutral is present, Code requires you use white for it.
blue for alternate switched-hot, if there's 2 switches involved or if red is in the box for other purposes.
yellow (solitary) for third switched-hot.
yellow (on a pair of wires) for 3-way travelers.
Etc.

This makes boxes make a lot more sense really fast.
Feel free to start your work by following the lamp blacks to their wire nut and marking all wires in that clump with red or blue electrical tape.  No need to mark the old lamp's wires obviously.