They upload while you download too. But normally download speed is much faster than upload speed, so it hurts your ratio. You could limit your download speed for a while, to let the upload do its job for your ratio.
Are you using uTorrent? If so, in the low edge's middle part of the window, you will see the speed at which your downloading, and the one your uploading at. Click on the download speed, and you'll be able to choose a number