How do you check transmission fluid?

Most vehicles have a transmission dipstick. Much like an oil dipstick. However, you want the Kia running and warmed up for a few minutes. Pull the stick, wipe it off, stick it back in all the way. Pull it out again and read the tip of the stick. Fluid should be red and clear like Kool-aid. If it's brown and smells burnt have it flushed ASAP.

All makes have different instructions. If you don't have an owner's manual they can be read on-line. Google it. As long as the level is fine, there is a school of thought that says don't change it, which differs from the advice of another poster above.

Flushing can be good or bad depending on who does it. Just add some if it's low and not discolored.