Dual Wifi Routers Setup

Hi, Good day tech guys, i am from the philippines and would like ask how to setup 2 wifi routers at home. I have a Zyxel P-660hn-t1q as primary and my linksys wrh54g or prolink h6300g to be used as secondary wifi router. How can i configure or setup my secondary wifi router to extend the wifi range from the ground floor to the second floor of my house.

Any suggestions will greatly appreciated and thank you in advance for the help