Open to below with stairs

[Colby]

Hello all;

I'm a beginner with this project (architect 2014) and I'm trying to create a set of stairs. I've successfully created the stairs in the basement, and they're showing up emerging from the floor at level 1, but I can't get the level 1 floor to disappear where the stairs are, so the stairs are emerging from the floor. I read in other posts that newer versions of the software automatically create the opening, but mine is not doing it for some reason. I've also seen posts about creating a room and setting the room to "open to below," but I'm not seeing the "Open to below" option anywhere. Can anyone help?

Thanks a lot.