To build on cybmole's (correct) advice, if you read other threads on this subject in the forum, you'll see two facts:
1/ Signal propagation in a house is dependent on materials, distance, objects in the way, placement of wireless router.
2/ With the exception of the latest BT Smart Hub, all routers provided by manufacturers are get you going devices with basic wireless technology, albeit to the latest standards such as AC (if that means anything to you). They all perform the same.
There are solutions to the problem of house construction/topology, which involve some modest cash outlay which we can come to when you've explained more.