as the title suggests how do i change the gearbox oil

as you look into the engine bay there should be a allen screw unsure on size approx half way up the box, the drain plug is a bolt and its on the bottom on the block side...... hope this helps

I believe there is no drain plug so the only way to empty the old oil would be to tilt the gearbox on a jack or by removing and allowing the oil to flow out that way.

You would fill through the hole until it runs over the lip.

As stoney has said or get yourself a cheap oil extractor and vacuum it out - that's how I normally do it and can get rid of most of it.

Not all gearboxes are filled until the oil is level with the filler hole so it might be worth just double checking how much oil it takes to fill and compare this when filling it.