An warm hello to all the Kia users

,
I am the happy owner of an Kia Clarus, nice car, big, comfortable and suited for holidais. That was until a few days ago, then the gear box started to make problems.
After checking here and there I came to the conclusion that the gear box olie must be replaced but I couldn't find any way to do it... I know where to fil the motor olie, brakes olie etc ..but nothing for the gearbox.
If somebody had the same problem I would really apreaciate any help.
Thank you in advance
Florin