How to (safely) retract and lower a 40' extension ladder?
Your ladder should have a rope and pulley mechanism for extension and retraction. Make sure you understand how it operates to prevent finger injury. Normally it's simply a matter of pulling down on the front rope to raise the ladder. To retract, lift the ladder a few inches using the rope, which allows the retention brackets to release, and lower the ladder extension with the rope.

Walking the bottom out to lay the ladder down isn't a good option. It puts huge torque on the person holding the upper portion of the ladder and risks damage to the building. 

A single fairly strong person can safely stand and lower a ladder by simply placing the ladder base against the wall our foundation and walking it up from underneath, or by backing away. 

Watch a firefighter do it.