The screws have little covers that need prised off (cover them as you do this because if it pings away you may never find it!)

The screws are plastic and go into plastic plugs on the car and may well be stuck solid. If they do snap, you can get new sets off someone on ebay for about £7.50 delivered.

The actual cowl parts are near impossible to find anywhere at sensible money though so don't forget the two wee screws - one on each corner piece - that are hard to see.