Tools, Sharpening and Power Machinery - foldable ladder

I've got a question on how to use a foldable Wagner Multi-Master ladder I bought at Home Depot or what should I use instead. I am working on the project where I remove all popcorn ceiling in my house and the toughest place is above the stairs, that's why I bought that ladder - hoping it will help to reach farther. Stairs are 8' high and 14' long and I can't even imagine what can I extend over that long of the span that would not sag or stable enough that I wouldn't break my knack. I also learned that even when the ladder is folded in the most weird way and looks like I could reach the ceiling, ladder's instructions say that you should not stand on or higher then second step from the top. In fact ladder seems to be unstable and does not provide a hood foothold. Please help with suggestions. Thanks.