Replacing the power-steering fluid is generally not included among the regular maintenance items list that should be performed; it is basically up to the owner to make the call.
When you take your car in for the routine maintenance, you may hear a sudden pitch for changing the power-steering fluid because the current fluid has turned black. Keep in mind that after a while the engine oil and the transmission fluid also become darker, so a deeper shade of red doesn't necessarily mean the power steering fluid is bad. Before jumping to conclusions, check for the manufacturer's instructions on replacing the steering fluid, and you won't probably find anything about changing the fluid.
You should keep an eye on the power-steering fluid reservoir on a monthly basis to make sure it has the proper amount fluid in it and that the system isn't leaking. Many vehicles have reservoirs made of see-through plastic, so you can check the fluid level without even having to remove the cap. In most cases the location of the reservoir is around the brake fluid reservoir in the engine compartment. The cap on top of the power-steering fluid reservoir has the type of fluid, that is required, written on it. Sometimes the manufacturer may use a specific type of fluid instead of generic ones found at parts stores.
If you are still worried about the power-steering fluid in your vehicle because of its age or appearance, you an easily change it at home without draining all the fluid and flushing the system. Find a preferably large dropper that will fit inside the reservoir and drain out as much of the old fluid as you can. Then, top it up with fresh fluid to the proper level. You won't be able to get the entire fluid out, but repeat this process a few times and you should be able to replace most of it.