Remove the back of the kindle.
Start with opening the back at the sides. Push your knife or tweezers in a bit deeper at the middle and twist them to push the glued cover part from the frame. Don't do this near the side buttons as you might cut the buttons' ribbon cable.
See this video from 0:33 to 2:00. Do not follow it any further as you don't need every step from this video to replace the screen!