I need help with getting a better wifi signal

So i just moved to my grandparents house, and they are in big country land in snowflake arizona. I bought a wifi router and hooked it up to their modem and everything and it is working. However it is pretty slow. I live in the basement and they have pretty thick walls since it is an old house so i know that could be a problem. Because the router is in the floor above me. And even their regular internt on their desktop runs pretty slow. So they had a guy from their internet comapny come out from channel1 i think it was to check everything out. He said pretty much the same thing i did about the thick walls but also that they have big trees around their house that block the signal to their computer. So I asled if there was anything at all i could do to better improve my internet down stairs. He gave me a super long ethernet cord and i ran it down into the basement from my wifi router up stairs and i hooked it in to my Apple tv. Because since i had been using it, while watching hulu it pauses almost every couple minutes, and it is absolutly awful and impossible to watch anything off of it. And unfortunatly connecting the ethernet cord did nothing to help and it is still runnig slow as ever. I asked the guy if they were to upgrade to a faster speed of internet if it would help at all because i know the internt speed they have right now is near nothing. So i know that is also probably an issue.

I am just a girl looking to have some wifi in a desolate farm land hahaha Is there anything at all that will fix my problem? Or am i just SOL..

Please i hope anyone can help me i am so desperate I cant be stuck watching the news every waking moment of my life haha