The capacity for the 6 speed is 1.9 litres, not sure about the 5 speed.
The car needs to be level!
Loosen the filler plug on the side of the gearbox, and then loosen and remove the drain plug on the bottom - let the oil drain out.
You do it this way so you know you can get the new oil in and you won't be left with a car you can't drive.
Refit the drain plug.
To fill it, either buy some clear plastic tubing - (make sure it fits in the filler hole and the tubing isn't too narrow) or by a pump.
I used the tubing, push it into the filler hole and then up the side of the car.
Fit a funnel and then pour the fluid in slowly.
Be aware that you might get some air locks, so make sure that you keep pouring until you've used more or less the correct amount.
When it's filled to the correct level it will start overflowing from the filler plug anyway.
If you've got the 6 speed box, you should only have approx 100ml left of the 2 litres you started with.
Refit the filler plug and you're done.