Draining the gearbox fluid for removal or renewal
If you can do engine oil, you can do gearbox oil
Underneath the car there is a Drain Bung
If you can reach - good
if you cant
jack it up and ensure its secure on axle stands

With your trusty catch bowl - sump nut tool - Crawl underneath
Highlighted in Blue it facing towards the rear of the car is the Drain bung
Remove and catch the fluid
Once drained - replace bung - Follow the Step of topping up or refilling the gearbox