Elevating, in this use, means that something lifts your mind: it makes you care about serious, intelligent, or moral things, as if you were being raised above everyday chatter. An elevating book, an elevating speech, elevating company. It can sound a little old-fashioned or preachy, and people often use it with a small smile, as a joke — “How elevating” — when the talk was actually silly or rude, meaning the opposite. The picture comes from elevate, “to lift up”: here it is your thoughts that are lifted, not your body. You will meet it in reviews and in slightly posh or humorous talk, not on a lift’s buttons. If someone is elevating the discussion, they are steering it toward bigger ideas. Though actually, the same -ing form can just be the ordinary verb (“they are elevating the box”), but that physical sense is not this one.