Screen replacement for a Samsung Galaxy S4 involves using a heat gun, set to the lowest heat setting, to heat the phone's screen for four minutes. Then, use a thin plastic tool to carefully lift the screen along the edges. Take special care not to damage the phone's digitizer or the bottom touch keys when removing the screen. Clean the digitizer using a microfiber cloth, apply new adhesive, and fit the replacement screen.
First, open the phone's back cover, and remove the battery, SIM and micro SD card. Use a heat gun that's set to the lowest heat setting, or a hair dryer, to melt the adhesive that holds the screen in place. While it takes about four minutes for a heat gun to melt the adhesive, expect a longer duration when using a hair dryer. Ensure the screen doesn't overheat by placing the heat gun at a safe distance from it and immediately shutting off the gun if you notice any discoloration.
Use the thin plastic tool that is included in the replacement pack to carefully lift the glass around the edges, starting from the top. Place a plastic pick in the gap to hold it in place. Reheat the glass as needed to ease this process. Work your way around the screen and take special care when removing the bottom part of the screen since the touch buttons are attached to the glass. Carefully lift the glass, and remove the touch buttons.
Use a microfiber cloth to clean the digitizer. Apply the replacement pack adhesive around the edges of the phone. Remove the plastic cover on the inner side of the replacement screen, and carefully fix it onto the phone. Return the phone's battery, and turn it on to test the results.