1. You need to take the undertray off - Be carefull as they are like rocking horse poo.
2. As you look at the front of the car, it is located (Not obviously) on the left hand side as you look (ie the drivers side) of the sump towards the rear of the sump.
3. You will find it is much easier to undo when the engine is warm (Steel plug in a steel insert in an ally sump!)
4. BE CAREFULL OF HOT OIL!! No matter how tidy you try to be, oil will go everywhere and I recommend the largest area of drip tray you can lay your hands on.
5. Depending on year, get a new sump washer as well - Some have some don't.