Gently spudge the power button connector off of the side of the device. Starting from the bottom right corner of where it is in the first picture is the best way to go about this.

Gently disconnect the highlighted ribbon cable from the motherboard.

DO NOT PULL THE MOTHERBOARD AWAY FROM THE DISPLAY HOUSING YET!

The last picture shows the ribbon cable connecting the speaker and headphone jack assembly. You do not need to disconnect this if you are only replacing the digitiser.