You have to remove the white back cover, SIM cards and MicroSD. You will see a bunch of phillips head screws on the black internal plastic, one of them is covered with self-adhesive paper, pay attention to remove that screw too. After removing all the screws you have to carefully take the middle black cover and the front part of the phone apart. Although the black plastic is flexible, you have to be careful, not to break it. You can use a plastic card, or special tool for disassembly. After removing the middle black cover, you can push out the lens from the inside, it is only fastened with a double sided tape. You can buy replacement lens from Aliexpress. Although it is also possible to remove the lens without disassembly, only by lifting up it's edge with a very thin flat screwdriver, I am not recommending it, as this will certainly damage the chrome frame.