The other type of assembly connects the springs to cables which run through pulleys and connect to the door (as illustrated below).
Wear safety glasses to protect your eyes from the possibility of a spring firing into your face. Close the door to reduce the tension on the springs. Replace one spring at a time before moving on to the next.
Attempt to lift the spring's hook from its anchor point with your fingers. If the tension is too great, try using the shaft of a medium/large screwdriver. Place the shaft into the hook and pull down on the hook and lift it off of its anchor. If necessary, find a leverage point for the screwdriver and pry the spring off. Unhook the spring from its other anchor point and install the new spring.
If you are replacing the cables or pulleys, first remove the springs. The cables connect to the door in a variety of different ways. Inspect the connector on the replacement cables to help you understand how they fasten to the door. The pulleys are typically held in place with one or two screws and are easily replaced.