How can I change video (or image sequence) speed (slow or fast) in blender composition? I want to use slow down effect in composition. I can't find any control. I found time node.
https://docs.blender.org/manual/en/dev/compositing/types/input/time.html?highlight=time%20node#example

But I can't figure out how to use it.
You want to use Time remapping, a quick google search for that will help you.  Also when I get to a computer I will update this answer.