If the footstool is on its side like this, we can not sit on it. So we say "lay the footstool flat" or "lay the footstool down flat"
What about do it the other way round?
Say a child has to move it to a different place and he can not lift it up easily because it's quite big a little heavy.
He should roll it.
To do that, the child needs to "stand up the footstool so that it is on its side". I am not sure if this is a correct expression. If it is, then it's a little long.
I am not sure when an object lies and when it stands.
Say, a chair is standing when it is in its correct position and a chair is lying when it is on its side.
But the above footstool is lying when it is flat?
and it is standing when it is on its side?