The original air deflector was making a 'flapping' noise when I drive the car and it was tracked down to this and found that it was broken. So I ordered a new one - FINIS code 1212560 - to replace it. The only difference I can see with it is it has a 'snoop' so I guess it's a new design by Ford. Click for bigger picture.
First, remove the old one by unscrewing the plastic screws - if you find it broken or loose, you can get a new one - FINIS 1007932 - and you will find it easy to pull out the old air deflector easily.
Now with the old air deflector off, you may want to clean the insides (dead fly, insects, etc)
Fit the new air deflector on, ensuring that the air deflector goes over the snorkel, as seen in the photo. That will ensure cold air will enter the snorkel correctly. If you put it inside the snorkel, you get less air going in. Screw them in.
Stand back and admire the new air deflector!