Remove the screws holding the fan enclosure in place. Mine had one at the top which screwed directly into the logic board, and another at the bottom (underneath the left yellow arrow on image 1). Place one hand on each end of the fan, lift straight up, and remove the fan from the enclosure.

Replacement Note: Before re-installing the front fan assembly in the enclosure, make sure that the fan cables are routed correctly in the fan channel. This can also be slightly tricky so pay attention to the alignment of the connectors on the fan unit and logic board.