Change the coolant of cooling system?

This depends on who you believe. Most companies will tell you that modern coolants are "lifetime" and never need to be changed. In reality coolant does wear out as the additives are depleted and it can turn acidic or even cause issues internally. As such I usually go by the older system and change out coolant with new every 50,000 miles. It's like the oil change intervals in modern vehicles. The companies get credits for reduced cost of ownership, so the more fluid changes they call for and the lower tire and brake wear issues raise those costs. So now you have folks whose job is to take an engine and run it until it reaches the time limits expected under warranty. So, if a car has a 50,000 or 5-year warranty and the engine and transmission make it to 60,000 with an oil change every 10,000 that is what they tell you. As long as it makes it out of warranty that is all they care about. How much past that it lasts isn't a concern. I tell most people that fluid changes are far cheaper than replacing drivetrain parts.