Nettie is wrong, turn it anticlockwise to unscrew it. put a piece of tape over the top of the fan otherwise the spring type washer will ping off & you may lose it. You can poke a large flat head screw driver down to hold the motor but be carefull not to damage the windings. once it is free it will turn off easily. Then screw back on & replace the spring type clip with the flat head screw driver.
Andy, November 2021