Several choices:
1: Get different wireless networking gear that has better range like some of the MIMO gear out nowadays. There's plenty of it on the market and it helps quite a bit.
2: Look at external antennas for your router - A directional antenna can help reception quite a bit but it can sacrifice general whole-house coverage.
3: There are signal boosters / range extenders that you could plug in somewhere on the 2nd floor to extend the range of your connection. Something like
this one would probably do nicely. They make others that are simply stand-alone and don't go over your powerlines, as well. Just make sure to buy it someplace you can return it if it doesn't work.
4: Reception is all about positioning. If it's not a laptop on the 3rd floor consider getting a USB-based wifi card and an extension cable. Just moving it around a few feet can make a significant difference. Same goes for your router, as well.
Good luck!
- G