The motherboard is mounted to the chassis by 8 screws, which must be removed.

Two of the screws are different from the others. The majority of them are 3.3mm. The outliers are 5.9mm(orange) & 5.7mm (yellow). It is recommended that you make a "Motherboard Pile"; a designated area for the screws needed to hold the motherboard in place.

Gently lift the motherboard away from the remainder of the device. Set aside in an anti-static bag if you have one. If not, avoid placing it on surfaces prone to static shocks (fabric or metal for instance).