To clean the camera (not replace), you only need to go up to Step 17. Just remove the bracket over the camera (two screws), then gently bend the camera out of it's socket, and clean the glass and the lens.
Total time for me 1:01:54 (start - finish)
1. Opening the device
2. Reassembly with small connectors. Also ended up with some dust on the LCD.
In my case, i found it easier to remove the sim - not sure if this was a placebo effect, but there you go!
also, there is a rubber seal around the screen - my experience is it should stay of the display, not on the main body.
In my case, my front facing camera was just foggy, and I suspected dust had got in there (was correct in the end). In this step I had to remove the shield (which you can see still attached in Step 16), which is over the camera itself. It was then possible to gently lift the camera out of it's socket and clean.