Would have to check and see if there is a genuine problem with that model. Your issue may very well be the fact that the signal is coming from a floor below. Concrete and steel are two enemies of wireless signal. Try moving the router closer to the roof of the ground floor / the floor of the top floor or near a window close to the room/s you need access in upstairs. Another option would be to get a wireless expander/range extender and place upstairs at the closest point that gives you signal. Another option would be to get another router and link them with a cable. Yet another option would be to get an outdoor antenna and mount between the too floors. And it goes on and on. If you say what your budget is like, if you can get parts overseas or not, or if you only want to deal with things with the current setup we can move forward. Bear in mind that the only ways to fix the issue would be to move closer to the router, get a better antenna or use an expander / other equipment - all of which will cost different amounts depending on your needs and budget. Waiting on your reply.
Knowing the solution doesn't mean knowing the method. Yet answering correctly and regurgitation are considered "learning" and "knowledge".