Wi-Fi Repeater Interference

[Giraffackle]

You guys have always helped me out, so hopefully you can once again 

 

About a year and a half ago we got a Linksys WRT1900ac because the router Verizon provides is just awful in terms of range. We don't know too much about networking, I just saw the router in a MaximumPC magazine and thought it looked good. It has performed very well and can even provide us internet at the bottom of our driveway (A bit slow though, but understandable). The problem is that this router is placed all of the way on the right side of the house on the first floor, and I am all of the way on the left side of the house on the second floor which means with all of the walls in between my Wi-Fi connection is terrible. I have another Asus RT-N66U router that I once tried to setup as a repeater for the Wi-Fi signal but it ended up absolutely killing the speeds which I'm assuming is caused by interference with all of the signals. 

 

My question is how can I setup the Asus router to extend the Wi-Fi signal to the left side of the house without it interfering and killing the connection. I have already tried power line adapters but they had issues of their own and I can not run Ethernet cables through the house because we are renting.

 

Hopefully you guys can help out and please try to explain your answer in a way that someone not too knowledgeable in networking can understand. 

 

Thanks!

[Giraffackle]

I managed to fix it somehow and both routers are working perfectly, no need to respond!