Hi Michelle
The trend is to move away from powder extinguishers indoors (although I have heard that there is an attempt to re-introduce them for some indoors applications in the standards), as the powder can be inhaled, reduces visibility and makes a mess. However, powder extinguishers don't have to be replaced before the end of their serviceable life. When it eventually comes to replacement it depends what your rooms contain. CO2 extinguishers have only a very narrow application and not great for general fire fighting, so if you have an office or retail application you would be better off with foam extinguishers that have been di-electrically tested or a water mist with de-ionised water. Both can be used on live electrical equipment up to 1000 Volt.
Harry