Verified answer

REMOVE ANYTHING THAT IS HOLDING THE COOLER IN PLACE AND THEN LIFT IT UP, REMOVE THE HOSE AND DRAIN THE CONTINENCE INTO A PAN.

There's a valve somewhere at or on the bottom of the radiator. Just open it and catch the coolant in a container. If the container starts getting full, turn off the valve and dispose of the contents, then open it again and let the rest drain out. Do not run motor with no coolant in radiator.

Why would you want to empty a cooler in a car for.