Use a Phillips screwdriver to remove one 4 mm screw and one 10 mm screw from each fan.

The 10mm fan screw won't actually come out, as it is attached with rubber piece to fan. Unscrewing it from the lower case will allow for removal, though.

Unplug both fans by gently disconnecting the fan connector from its motherboard socket. If you have trouble, gently wiggle the connector to loosen it.