First, if you can move your router up from the basement, that's the best option. Next would be to connect a WAP (Wireless Access Point) with wireless-N to the router, and if possible run a wire from the router upstairs to where you could put the WAP.
I have internet through our cable company. I am suppose to have the medium speed they offer but when when we try to use netflix or play on line games it is so slow it constantly is streaming/buffering so we can do either . It is also slow on the main level where the modem is. Any suggestions?