1997 Range Rover air release

How do you go about releasing air from the cooling system? The radiator, water pump, and engine were replaced a year ago. The car started to run hot yesterday and when I pulled over I removed the upper radiator hose and air flew out along with a little coolant. After letting it rest while off I poured coolant into the car (while running) and then it ran just fine like nothing ever happened. I replaced the thermostat that day, so I am having to see if that was the problem, but in case it wasnt how do you bleed air from the system?