It seems that for replacing the lower radiator hose, I just need to drain the radiator. What about replacing the upper hose? How often to most people replace them?

 

Until you feel them saggy.....If that the right word.........

 

If you need to change both you best bid is to clean flush the radiator.

My 2 cents

AA

 

When the engine is cool any rad or heater hose that feels soft or spongy are suspect. Compare the look of the "hot" rad hose from when it is cold to when the engine is hot and running. It will expand somewhat but if it has local bulging or "ballooning" right adjacent to the clamps it may be suspect. I doubt that you will ever have to change the "cold" hose unless it has physical damage. They usually last the life of the car.