Just did this on a 2014 1.8L with automatic.
I used Citgo Dextron VI certified fluid because it was on Amazon for less than $50 for 12 quarts. Haven;t seen it that price for months now. I bought 2 cases . . wish I bought 4. Any Dextron VI should be good.
The same procedure is like on the Chevy Cruze automatics. . find YouTube videos showing how to drain and check side view port from driver side wheel well. Do NOT open side view port bolt until after filling, running the engine to warm up, and then check side view port on a perfectly level floor. Just measure what you take out for the each draining. . . . will be about 5.3 to 5.4 qrts.
It will drain about 5.3 to 5.4 quarts of ATF each time. Drain after driving and fluid is warmed up
You just drain using the small drain bolt on bottom of tranny after fluid is warmed up! Let it drain and then refill 2 or 3 times after driving a couple days or so between each fill. Doing it 3 times is best as it changes most of the fluid out.
Watch several of the YOuTube videos with the 6T40 trnsmission. . The fill cap is a black plastic cap on top ot the tranny. Need a long funnel to put into that and pour in from above.
BE careful, and do not over tighten the bottom drain bolt. It has some thread sealant on it originally and is also a tapered type pipe thread it appears.
NOTE: There is another way to do this all at once. IT involves disconnecting the output line from the transmission to the radiator transmission cooler fitting. Have to make sure it is the output or "feed" line to the cooler. Think it is the lower one. Then you have to add some plastic tubing to the output fluid line, run it into a large pan (12 quarts at least), have funnel and open fluid jugs handy, while someone sits in the car, starts it up and watches your commands to stop if needed.
Not for novices because you have to keep up with adding fluid as it runs out the transmission output line .