Mine didn't come with instructions.... I figured out how to do it when I detail stripped my glock.
Field stip the Glock. Push and hold the firing pin into what's left of the chamber to take pressure off the backplate. Place your thumb over the back of the slide as you remove the backplate to catch the extractor spring. The extractor spring will come out of the top right of the slide.
Otherwise, it's really hard to get it off and the spring goes flying.