There are right ways do do things and there are wrong ways with almost nothing in between.
Extending wifi two floors.
There are plenty of ways to extend wifi range outside from floor to floor or from building to building without having to make hefty investments or become a certified network engineer.
Frankly as we see it your friend probably has 3.
2 connect one of the powerline network adapters to an open lan port on each router.
3 plug both adapters into the nearest electrical outlets.
There are a variety of different signal issues that can come up when trying to provide comprehensive wireless coverage to your entire home.
Think of it this way you live on the second floor how strong is the signal there.
Almost all technology including wifi is pretty black and white and leaves very little to no room at all for interpretation.
Wifi uses radio signal on the 2 4ghz and 5ghz band to extend network connectivity to end user device.
The very simplest approach to extending your wi fi network is to add one or more range extenders.
Connect the two routers.
1 place the second router in a central location on your home s second floor.
Boosting wifi signal from neighbor by extending with repeater.
You probably aren t getting full bars with 2 floors between you and the wifi source.
These small units plug into an electrical outlet and then can be configured to repeat the signal.
Plug one end of the ethernet cable into any lan port of the primary router then plug the other end of the cable into the lan port on the back of the second router.
These two extender options are for sending a wireless signal a far distance such as across the street from the neighbor s house.
It s not very likely that he ll get anything at all.
They rely on line of sight and really can cast a signal the furthest.
Your options vary based on the type of environment you re in the type of equipment you re using and the results that you want to achieve.
If you are creating a lan to wan network plug the other end into the wan or internet port on the secondary router.
Drywall can degrade a wireless signal quite quickly especially if the signal has to pass through extra insulation and piping such as a wall shared by a bathroom.