Do you have the guide booklet that came with the laptop?
Essentially, you will have to place the laptop upside down. Then unscrew the screws from the bottom of the laptop.
Pull out the keyboard and unplug the internal wires of the keyboard.
Do similar to the trackpad.
Replace the parts and check if everything works properly.
Screw the screws back to the bottom and the job is done.
I hope this helps