Here is another step by step post on how to diassemble the Tokyo Marui MP5K.
We are going to turn this MP5K into the one pictured above.
Remove this pin by pushing the nubs inward so you can pull it out on the other side.
Now pull out the front grip which also serve as a handguard. Inside you can see the fuse and the connector to the battery.
Now also remove these two pins that holds the back plate.
After removing the back plate, carefully pull out the two wires that connects the gearbox to the upper receiver.
Now using a small phillips screwdrver remove this screw to pull out the selecter switch on the left and pull it out on the right.
I forgot to take photo, but the next step is to remove the pin above the magazine catch, this pin holds the lower and upper receiver together.
Now turn it upside down and remove these two screws under the grip to gain access to the motor.
After removing the screws, the grip plate should come off easily. There is also a metal disc, this is very important to your gun. This disc serves as a motor tension when adjusting the meshing of the motor's pinion gear to the bevel gear.
Then remove the two wires that connects the motors.
Remove the motor and remove these two screws inside the grip.
Once all the screws are removed, you can pull the lower receiver out.
Then remove the gearbox carefully.
And there you have, you should have all the parts as shown above.