Undo the big white nut all the way until it jumps up on the spring.
With the big black handle still in place push down and forward on the top of it (this may need a bit of brute force and ignorance) until the wheel and cradle falls to the floor.
Keep you feet back from the car as it literally free falls
Drag the wheel out from under the car and unclip the cable from the cradle.
To put it back put the wheel back on the cradle, and clip the wire back in the slot....pull up on the handle until the thread of the cradle is visible in the boot....while holding in place with the handle, screw the nut back down on the tread until it clicks.