keep pulling until. There are 4 rubber mounts as Dragon explained. The best thing to probably do is tug on each corner firmly, but not wildly. The cover should come off, nd make sure you dont lose any of those rubbers on the cover.
Lumns forgot to post up the link to his engine trim DIY he made a couple months ago...seems some of the pictures dont show up anymore, but if you click on the apparent links you'll see the shots taken...here it is: