I sometimes stick a screwdriver between the subframe and the plastics and use it for leverage, but once you take the screws off you should be able to tell if it is loose. it wont just come off by any means, you have to kind of pull the edge from around the subframe. It is hard to explain, but it isnt too hard so I'll try...
you have to grab the tail plastics down by where it meets the frame just under the air box. With one hand on each side pull the plstics outward. As you're doing this, slide the plastics toward the rear of the bike and once you get to a certin spot it will come free. OR you can do this with one hand on one side. Just slowly move your one hand toward the rear while you pull to the side. as the tension gets tighter you will be able to pull up and get the lip of the tail plastics over the undertail plastics/ subframe.