Most manufactures recommend that you change out your engines coolant every 60,000 miles but most people don't do it that often and only change the engine coolant when they're changing the radiator hoses or heater hoses.
I change my coolant whenever I change out my radiator and heater hoses which is every 70,000 miles or before I head out on a long road trip that is over 200 miles.
If I'm going on a road trip that the distance is longer than 200 miles then the coolant as well as the radiator hoses and heater hoses get changed just so I can have peace of mind knowing that everything with the coolant system is working properly.