Turkey baster method:
1) with the engine off, using a turkey baster, drain the PS fluid reservoir. Refill with fresh fluid.
2) run the engine. Repeat step (1).
3) go inside and watch American Idol. Or cuddle with your wife. Of your neighbor's wife.
The thing people don't understand is that the power steering pump runs continuously, and the fluid is constantly recirculated and flows freely. Then, when you turn the wheel, one side of the piston in the rack becomes pressurized by diverting the pumped fluid to that side of the rack. By following the "turkey baster" method, you'll essentially be replacing alomost all of the fluid.
I've attached a few drawings for illustration. As you can see, there is no clutch in the pump assembly. It's a direct link from the serpentine belt to the pump vanes. Fluid circulation is constant as long as the engine is running. The valve in the rack determines whether the fluid recirculates or compresses in one side of the rack.
Oh, and READ TEXASES POST. Purging and freshening brake fluid is 1000 times more important than purging and refreshing PS fluid. You lose your PS fluid, your steering gets harder. You lose your brake fluid, your entire life gets harder.