Hello, GM does not list a procedure for changing the power steering fluid. They only list a procedure for bleeding the system when fluid needs to be added. There are a lot of places that do a power steering fluid flush, but they have a machine similar to a cooling system service machine that pumps in new fluid as the old fluid is pumped out. With out having the benefit of one of these machines, the best a person can do is to remove a hose from the power steering and drain the fluid out that way. Then fill the system and bleed it per GM instructions. The lower in the system the hose is that you remove, the more fluid you will be able to get out.
Important: Power steering fluid level must be maintained throughout bleed procedure.
Important: With hydro-boost only, the oil level will appear falsely high if the hydro-boost accumulator is not fully charged. Do not apply the brake pedal with the engine OFF. This will discharge the hydro-boost accumulator.
Vehicles equipped with hydro-boost systems or longer length power steering hoses may require turns up to 15 to 20 stop to stops.