DIY, In order to replace the left tail light assembly on a Kia Rio 2010 you will need a 10 mm socket wrench. The repair is very easy. It should not take more than 10 minutes.
Basically you just have to open your trunk and remove the tail light assembly cover, as shown in the picture below.
After you have finished that simple task, you should see four bolt nuts, that are securing the back light assembly. Now, using your 10 mm socket wrench, you have to remove the nuts and you will be able to detach the assembly. The hardest part of this repair is not to loose the nuts into the body of the car. Getting them back could be a tricky job. In the last part of the process you just have to disconnect the electrical harness and you are done.
Detaching the assembly might help you if you want to change some parts of it or when you need to replace burned light bulbs. You may want to do that in case you cannot get to the bulbs. Otherwise, replacing a bulb is very easy. You just have to rotate the gray plastic parts counterclockwise and you will be able to remove the bulb. Do not forget to install everything back with caution, because you can drop and loose into the body of the vehicle, the nuts that hold the assembly.