Work your way around the perimeter of the phone with a spudger and plastic opening picks to free the clips that secure the rear case to the display assembly.
A metal spudger is pictured, but it is best to use a nylon spudger to prevent marring the device.
Be careful not to lose the power button: it sits loosely in the top of the lower chassis.
Significant force may be required to pry the casing apart.
Use an iOpener or a heat gun to loosen up the adhesive securing the motherboard to the display assembly.
Use a plastic opening tool to gently pry the motherboard free of the display assembly.
At this point, the bottom speaker is still attached to the motherboard. If you are only replacing the motherboard, refer to the bottom speaker guide to swap your existing speaker to the new motherboard.
thanks for the instructions. i dropped my m8 and the power button wasnt responding at all and volume down wasnt either . i dissassembled the phone ( maybe i shouldnt have used my swiss army blade, left dents in plastic) using this guide..and pushed all the connectors into firmly and it worked again . thanks a bunch