Remove the 3 Phillips #0 screws from the fan bracket.

Lift the fan up and place it back down above the heatsink.

Do not fully remove the motherboard. As there is hidden cable on the underside that could be damaged.

The heatsink has a strip of adhesive on the underside securing it to the plastic body.

The motherboard can be lifted from the side and and then to the right to free the I/O port from the enclosure. Some force may be required to release the heatsink.