The hardest part of this repair is, without question, removing the back phone case. Expect a bit of a battle, and keep in mind that the plastic is surprisingly flexible, and unless you are pulling extremely hard, you shouldn't have to worry about snapping pieces

Before you go further, make sure you remove the sim card & tray - the case back will not come off without it. You can use a paperclip or a SIM removal tool - it's a relatively shallow slot

Remove the 2 torx screws on the bottom of the phone (size 5)

You may need to use pliers or a magnet to convince the screws to leave the phone case, they tend to get stuck