I'd forget there is any WiFi when it's in a basement. There are so many web pages about this that I will not duplicate it again. If this was mine I'd move the router WiFi to old reliable 802.11g mode ONLY and pick a channel. Now that should get you coverage in the basement.

For upstairs I'd deploy another WAP (even the 20 buck TL-WR702N will do then for starters leave it on 802.11g and another channel to spread the WiFi load.

-> TORRENTS mean the death of a network. Not only do they suck up all bandwidth but can cause DOS attacks. If you want this to work, you won't go near torrents.

Yes there are some that can't kick the habit so they can't be helped,