If you are trying to unscrew the base of the housing but it is not budging, chances are you have mineral deposits built up on the threads.
To solve this, simply soak the housing in hot water and vinegar solution. You will only need enough water to cover where the base and top of the housing meet. Use the hottest water from your tap then add 1 cup of vinegar. Soak the housing for about 5 to 10 minutes before you try unscrewing the base again. You may need to repeat it a couple of times.