This is the thorough way to do it. This is also recommended by steering rack remanufacturers to flush out debris from their units after installation.
Flush Power Steering Fluid Exchange
You'll need a helper.
1. Lift front tires off the ground.
2. Disconnect the ps return line at reservoir, drain ps reservoir.
3. Plug open connection at the reservoir.
4. Secure the return line to a generously-sized container (at least one gallon). If needed, add a length of hose.
5. Fill reservoir with new fluid.
6. Line up your bottles of new fluid for quick pouring.
Here comes the fun part...
7. Have helper turn car on, and immediately have him go through full range of steering motion (left and right) and shut off car, all the while you are trying to keep the reservoir filled.
8. Button everything back up.
9. Clean up mess.
10. Top off fluid.
The front tires must be off the ground so the system is unloaded, otherwise a lot of fluid is forcefully pumped out. The return line must be secured to prevent a big mess. Keep at least a gallon of ps fluid on hand. The helper must know what they are doing.
I strongly recommend using power steering fluid rather than the Dexron stuff that is probably recommended for your vehicle. Modern Dexron formulations are different than the Dexron formulations present at the time when your car was built. Power steering fluid is the same as Dexron, but without the additives that may be harmful to the steering system.