The upper case is secured by magnets.

Grip the top edge of the upper case above the keyboard and lift straight up to release it.

Don't try to completely remove the upper case, as it's still connected to the laptop by a cable.

Lift the bottom edge of the upper case up and away from the laptop, taking care to not strain the ribbon cable underneath.

During reassembly, lower the upper case onto the lower case until the magnets snap into place and it lays flat.

Check that the upper case sits flush around the entire perimeter. Any gaps between the upper and lower case near the screen could damage the screen as it closes.