Take off the exterior trim, followed by interior trim with a wide pry bar.
Remove any screws inserted into the jamb with an electric or Phillips screwdriver.
Crank the casement window open -- notice a pivot assembly on the top and bottom of the window. Cut the metal pivot pin attached to each assembly with a sawzall or hacksaw blade.
Pull the entire steel casement and frame out with your hands. If you can't get a good grip on the frame, push the frame out toward the exterior with your hands or hit the bottom of the frame with a hammer to unseat it. If in a highrise building or second story of a house, avoid pushing the frame -- pull the frame into the interior.
Insert the blade of the sawzall in between the interior window and frame if you are having trouble removing the window. Power on the saw, then move it down in between the seam to cut all nails securing the window to the rough framing. Once nails are cut and the window is loose, pull it out with your hands. Then pull out the frame.