I had a similar issue at my house. Router in the basement, bedrooms had weak wireless. I already had ethernet running to my desktop upstairs and did what ExDilbert explained. Second router as a switch/wireless access point. Works mint. Have strong wireless throughout my house now. I run the bands on different channels so there is no crossover.
I use my Nighthawks AC 5ghz band exclusively for my laptop(it's in my living room directly above the nighthawk). It's as fast as any wired connection in my house. Everything else runs on 2.4 on either router or 5 ghz on the second router
Sony 75" X940D, 7.1 Klipsch, Onkyo TX-NR656, Xbox One/360, Nvidia Shield Alienware Alpha, Arris Gateway, 42" Samsung