There should be a small hand latch underneath that releases it. Some steps have a round extrusion where you put your hand with fingers underneath you pull towards you. Older ones are easily stuck.
If you lay down to look underneath place yourself off to one side or other. When they release the come out with some force. Once it is down make sure it is locked ( pull outward) in before you step on it do it doesn't collapse.
Sorry if that sounds vague.