How many miles has the car done?
The box holds about 9.5 litres, but you will only get about 6 litres out on a drain.
You need to drain it, fill it, drive it, drain it, fill it, etc, until you reduce the original oil as much as poss.
I'm going to change mine when it warms up a little. I've bought the filter, o-ring and gasket, and will be buying 20l of Esso/Mobil ATF LT71141 (about £170) so I can do 3 changes.
My car has 52k miles, so I'm doing this before it gets to the stage yours is at!