Ever so easy, did mine yesterday in about 5 minutes. A Google search will bring it up, but basically undo two screws holding the plastic panel on under the glove box. You will see a ridged cover near the back of the footwell, this pings off from the larger end nearer the centre of the car. Pull the filter out. Put new filter in and replace everything. Hoover the leaves & detritus up that fall out on to the footwell!
Make sure you get the right one though, the auto air con ones are different.