That red handle is a catch (there are three stops). The red handle is the thin, red, upside down U-shaped thing, not the handle to push it around with. Pull it back before trying to let it down. You might need to pump up once before you can pull the red handle back.
The catch has three stops on the black frame, so that the weight is not held by the hydraulics (the stops are along the side on the black frame), if you need something elevated for a period of time.
You might need to press down on the platform, while holding the release pedal (gravity might not lower it alone).
I could shoot a quick video, if you need.
Post edited by kirkgun: clarity