Fairly easy. Remove 4 rubber covers inside lid. remove 4 #5 torx screws. Carefully seperate outer cover from phone.(sim card or similar works to pry it apart)
Carefully lift(pry) glass away with card. Caution, don't use your fingers as glass can shatter and cut. Clean up excess glue.
Replace outer cover and secure with screws. Align and stick new lens. Install rubber screw covers.
i've done the one on my wifes phone twice and i dont have to take the housing off. the glass is basically just glued on if u can get something thin enough to pry it up it will peel off.