Without a pic I can't say for certain but most of the screens are held into place with a black or grey rubber bead that rund the entire perimeter of the screen. You can normmally get a very small screwdriver or awl and pry it out. Once you get it out pull it gently out of the frame. If it breaks that's ok because you can buy more at Home Depot. Once it's pulled out the screen material can easly be removed.
Got th HD and buy replacement material and install. If you've never done this before you might want to get the little rubber bead installer thingy majig. Looks like a pizza cutter. Ask one of the guys at the store and he can explain it to you. In all you spend about 10 bucks.
2004 Cardinal 33CKT
2006 Ford SDD F250 CC 4WD