Dave;

I'd have a look through the metal grate with a light to see how much flotsam and biomass has accumulated...if you don't see a lot, you might go with the "If it ain't broke..." technique and leave well enough alone, because...

...they are secured in-place by spring clips which may/probably, because they are high-carbon spring steel, have developed surface rust, which weakens them...this means that they might break if you are unlucky or force them during removal attempts...also, the force necessary to remove, if applied unevenly, can bend the soft alu cowl frame into a pretzel...another reason not to remove if you don't have to...

Having given all the reasons I can remember not to remove cowl...as far as removal technique, it's been a while, but from memory, if I had to remove one I'd locate the clips by inspection (I believe there are 2 or 3 X 2 sides), spray a lube (like silicon or thin oil) in the area to encourage clips to pop over the body edge, then use a stiff putty knife (maybe 3...one per clip! on the forward facing side), taped to prevent scratching paint, and slid between the cowl trim and body, to evenly pry at each of the spring-clip locations until they pop over the body edge and release...

Use this advice with extreme care and caution and at your own risk!...feeling and judgement you used on your first girlfriend is called for here (if you can remember that)!!! If someone can post a better technique with less risk...I'd love to see it!

Good Hunting!