Which router setup use should I use? Turn wireless router off & use as a switch

I am buying a new router (Netgear Nighhawk X6) that should be able to handle the dozen or so wireless devices we have as I believe Im overloading the 2 olders routers capabilities and/or to eliminate conflicts between the 2 routers

Currently, I have two wireless Netgear RangeMax routers, one on the south side of the house where the cable enters the house in my office and one in the center of the house that I had to put in to reach the garage/shop side of the house.

Q1) Can I or should I use one of the old routers as a simple switch (and hardwire the desktop, printer and Xbox in my office and use the 4th port to send the signal to the new improved wireless router in the center of the house.

Q2) Or should I forward the main line directly to the center of the house because using the router as a switch as above will dilute the internet speed currently at 50mps from my provider?

Also, how do you turn off the wireless portion of the router to use it as a simple switch?