Disco 2 Auto Gearbox

Hi,
I have to change the Auto gearbox oil on my Disco 2.
The manual gives the capacity as 9.8 Ltrs can anybody tell me how much actual oil I will need as all of the old oil will not come out when I drain down and I dont want to buy more oil than I need as I am thinking of putting synthetic oil in.
Thanks for your help

About 5 ltr. i hope u know the procedure(while engine running, moving the selector through all gears up and down).... but it's good to know what kind of oil u have within to put the same ... normally it must be ATF dexron IID or III

Thinking of doing an oil change on mine too, but what about if you dont know what oil has been used before as im not going to be able to get all the old stuff out...

Then use the recommended: ATF dexron IID or III