Well according to the User Manual,
The Fluid Capacity is 4.0 Ltr.
Drain and Refill Approx. 1.5 Ltr.
ATF Dexron II or ATF Ammix Multi is to be use
If you are going for the complete drain then,
1. open the chamber
2. clean it Petrol completely
3. Insert new gasket
4. Fix it back
5. Pour the new Gear Oil
6. Check the gear box by putting it in all the gears
7. Drive the car for 1 km
8. Check the gear oil again and refill accordingly