For a straight forward answer, yes you can extend your Wi-Fi using a D-Link or Linksys (Router) with a 5 Cat Ethernet cable run from your modem to the upper part of your house to the router.
When you set up the router, use the same user name but with a number on the end with the same password to make it easier to remember.
Main Modem: User Name: Dunkin
Password: Donuts
Guest: User Name: Dunkin2
Password: Donuts
Router: User Name: Dunkin3
Password: Donuts
This helps with sharing the modem without over burdening the in and out throughput's!
When configuring the wireless setup though the router, change the wireless setting from (7-2.452GHz) standard to another setting to reduce conflict between Modem and Router.
I have so many things connected to my Network:
3 Directv DVR boxes
2 or 3 laptops (mine, my brothers and nephews)
3 Smart phones
2 Blu-rays DVD Players
Epson Printer
PS3 and PS4
WII
Break up your Network connections to what running on each level on your home for the strongest Wi-Fi signal accordingly.
The first picture is the Modem, the second is my router and the third my network screenshot.
For router security, change the password unless you like sharing with the neighborhood allowing everyone to piggyback and enjoy free wi-fi!
