Provided you use recommended parts and oil, your car warranty stands. The Moss-Magnusson Act applies here.
If you have a metric socket set, you will just need a filter, crush washer and filter wrench.
The drain plug is a 17mm.
The Filter wrench is an 80mm 15 facet/flute wrench which you can buy from Advance Auto Parts (Part # W50468)
Torque values: Kia has a range for the filter and the drain plug.
I used just over the recommended median value for both.
14Nm for the filter and 40Nm for the drain plug (easy to remember!).
You will find that when you remove the filter, oil runs down the back of the plastic floor pan!!! Next time, I will insert a folded up piece of Aluminum foil (about 8X8") upwards into the hole and allow it to fold around the hole and hang down a little. When you remove the filter, it should not allow the oil to splash backwards into the plastic pan.
IMHO, it behooves you keep a log (using the KIa service book in your glove box!) and retain all parts and oil receipts. If you buy genuine Kia filters and crush washer, which are very reasonably priced, and the specified oil (I use Mobil1 5w30 here in Texas), you really cannot get into trouble. Being as I am in a small town 70 miles away from the nearest dealer, I bought my accessories (rubber mats and mud flaps) plus oil, air and cabin filters and crush washers from Deland Kia in Florida. Nice folks, great prices, good service.
I do have one service "GOTCHA" for Kia Optima owners doing their own servicing:
When they installed the drain plug, they sprayed over the plug and crush washer when they sprayed the oil pan.
So, when you remove the drain plug, it appears that there isn't a crush washer (or you think you dropped it in the oil!!! WRONG!!! You will need to (carefully!), pry the old crush washer away from the drain plug BEFORE installing the new crush washer. Of course, if you aren't as anal as I am, it isn't a problem! LOL
FYI - A few years back, I had a warranty issue with Toyota and I supplied them with all receipts (I used Toyota filters and Mobil1 oils, and my service log. They didn't fight me at all......