Here are the official instructions printed out for me by my dealers service dept. You should probably never need to do this. I screwed up and mistakenly drained the fluid in my trans by mistake. 
The guide says if you have severe use of your vehicle then you should replace ATF every 60k miles.
elntra tranny info by Doug in Idaho, on Flickr
You will need aprox 5 liters of transmission fluid. Use only the type specified in the back of your owners manual. This cost me $20 a liter from my dealer. You will also need a long narrow funnel. The instructions also recommend replacing the gaskets on all 3 plugs when doing this procedure.
Step 1: Remove the transmission drain plug from bottom of transmission case. This will drain aprox 5 liters of fluid. Allow time for all fluid to drain.
Step 2: Re-install drain plug and tourqe to 34.3 - 44.1 NM (3.5 - 4.5 kgf.m, 25.3 - 32.6 lb-ft)
Step 3: Unscrew filler eyebolt (see below...front slightly to the right of the engine). I found that the my socket wrench extension fit perfectly into the square opening in the middle of the eyebolt.
elntra tranny info by Doug in Idaho, on Flickr
Step 4: Insert your funnel into the opening and start adding fluid very slowly. I found that it liked to back up and overflow if I went to fast. It took about 30 mins for me to get all the fluid in without it backing up and out of the opening. The instructions call for adding 5 liters but the service counter guy recommended going with only 4.5 liters at least until you can check the level.
Now time to check the fluid level. The instructions say this is easier with vehicle on a lift.
Step 1. Start the engine (don't step on brake and accelerator at same time.)
Step 2. Confirm the temperature of the A/T oil temp sensor is 50-60 C (122-140F) with the GDS.
Step 3. Shift the select lever slowly from P to D then D to P and repeat once more at idle. Leave in each position for at least 2 seconds.
Step 4. Lift the vehicle then remove the oil level check plug from the front side of the transmission case (see first diagram above)
Step 5. (note vehicle must be at a level state) If the oil flows out of the overflow (level check) plug in a thin steady stream then the oil level is correct. If excess oil flows out in a thick stream you have an excess fluid level condition. If no oil flows out you have a shortage situation and need to add additional fluid.
Step 6. Once the level is correct tighten the overflow/level check plug and then re-install the eyebolt on the filler opening. Torque to (4.9 - 5.9 NM (0.5 - 0.6 kgfm, 3.6 - 4.3 lb-ft)
Step 7. Clean up any fluid on painted surfaces in the engine bay as fluid is corrosive to paint.
Step 8. Beer!
The guide says if you have severe use of your vehicle then you should replace ATF every 60k miles.elntra tranny info by Doug in Idaho, on Flickr
You will need aprox 5 liters of transmission fluid. Use only the type specified in the back of your owners manual. This cost me $20 a liter from my dealer. You will also need a long narrow funnel. The instructions also recommend replacing the gaskets on all 3 plugs when doing this procedure.
Step 1: Remove the transmission drain plug from bottom of transmission case. This will drain aprox 5 liters of fluid. Allow time for all fluid to drain.
Step 2: Re-install drain plug and tourqe to 34.3 - 44.1 NM (3.5 - 4.5 kgf.m, 25.3 - 32.6 lb-ft)
Step 3: Unscrew filler eyebolt (see below...front slightly to the right of the engine). I found that the my socket wrench extension fit perfectly into the square opening in the middle of the eyebolt.
elntra tranny info by Doug in Idaho, on Flickr
Step 4: Insert your funnel into the opening and start adding fluid very slowly. I found that it liked to back up and overflow if I went to fast. It took about 30 mins for me to get all the fluid in without it backing up and out of the opening. The instructions call for adding 5 liters but the service counter guy recommended going with only 4.5 liters at least until you can check the level.
Now time to check the fluid level. The instructions say this is easier with vehicle on a lift.
Step 1. Start the engine (don't step on brake and accelerator at same time.)
Step 2. Confirm the temperature of the A/T oil temp sensor is 50-60 C (122-140F) with the GDS.
Step 3. Shift the select lever slowly from P to D then D to P and repeat once more at idle. Leave in each position for at least 2 seconds.
Step 4. Lift the vehicle then remove the oil level check plug from the front side of the transmission case (see first diagram above)
Step 5. (note vehicle must be at a level state) If the oil flows out of the overflow (level check) plug in a thin steady stream then the oil level is correct. If excess oil flows out in a thick stream you have an excess fluid level condition. If no oil flows out you have a shortage situation and need to add additional fluid.
Step 6. Once the level is correct tighten the overflow/level check plug and then re-install the eyebolt on the filler opening. Torque to (4.9 - 5.9 NM (0.5 - 0.6 kgfm, 3.6 - 4.3 lb-ft)
Step 7. Clean up any fluid on painted surfaces in the engine bay as fluid is corrosive to paint.
Step 8. Beer!
