Although below it says that you simply do the reverse to reassemble, be aware that the home button has to be very carefully positioned else it tends to hold the screen up and it won't work reliably. Secondly, you need to clean off the glued areas on the frame very thoroughly, because they pucker badly when taking the screen off. If you buy a reputable screen, included with it there should be a couple of double-sided sticky pads, shaped to fit the ends, which will hold the screen down.

It isn't obvious from the description that the major glued areas are at the ends, and particularly the corners. Further, the glass screen itself is overlaid with a thin, flexible cover, and this extends from the glass edge about a centimeter top and bottom. The real danger of screen break is at the sides, where the underlying glass comes very close to the edge of the plastic cover. What you see in the picture is OK, the spudgers going under the cover but not too close to the glass at the end. You need to lift both ends of the screen very slightly before easing the sides up. And the glue patches at the ends are pretty tenacious.