Place the NUC upside down and select a PH2 Phillips screw driver bit

Start by using a Phillips head #2 screw driver to remove the lower screws on the lower case door.

These screws are held in with retainers, so they won't fall out when you flip the lid.

Lift the door, and keep an eye on the cables that connect to the NUC's motherboard. These cables are the power and data cables for the 2.5" hard drive bay.

Carefully unplug the cables from the motherboard, and set the bracket aside.

In the last photo, the slot for a blade SSD is marked with a red arrow. This is where you would install the blade SSD, and use a screw to hold it in place.

Change the screw driver bit to the PH1 one.

Unscrew the V-NAND SSD and carefully slide it out of its connector.

Change the screw driver bit to PH1

Unscrew the screws marked in red circles

Remove the WiFi and Bluetooth antenna cables (be extremely careful when doing this otherwise you risk to rip the base contact terminal off the PCB)

Remove the stereo mic cable from the motherboard connector.

Pay attetion to the WiFi cable hidden under a black piece of tape

Not all are necessary only the two depicted.

Use a pry tool to lift the motherboard from the casing

Marked with red circles the dust signs evident on first sight