Easy enough to change the oil.
Get vehicle up to normal operating temperature.
On flat surface loosen sump plug (19mm)
Wait until drips stop. Refit sump plug.
Add approx 3.5 litres J4 auto trans fluid to gearbox through dipstick hole ( long thin funnel needed)
go for a 5 minute drive to ensure oil mixes.
Start at the beginning and redrain.
This will ensure most of the old oil is flushed through. if after the second drain it does not look BLUE like the new oil, then repeat process until it does. If the oil is not that dirty, then twice is normally enough. But if it hasnt been changes for a while then more will be needed.
You WILL need a new sump plug washer as well, but dont bother changing it until you are sure the oil is clean enough that you wont have to do it again.
When it is clean enough, on the last fill only put 3 litres in. Run engine, go through the gears (P R N D N R P) a few times then check level It will be near the C (for cold) mark. If not add some more, then go for a drive to warm it up again. Check level again, need to be on the H this time. Inbetween adding and checking, go through the gears each time, and let it sit for a minute before checking to let the oil run out of the dipstick tube and level out.
It is VERY IMPORTANT you use the correct oil. DIAQUEEN J4 is expensive, but other oils are not compatible. Some brands do CLAIM to be compatible , but they are not.