Just changed mine, plug removed and at best got 3 litres out, replace the exact amount, do not overfill, as stated to change the lot 13 liters thereabouts iirc it's a dealer job, or you can repeat the process 4 times they say by driving a short distance, which mixes the old with the new. Not noticed any difference since doing it. Took the easy way out though.
An older model but the same method
https://www.youtube.com/watch?v=L7_RsnD8hAU