I had posted somewhat of a "tutorial" about BT some time ago, so this may help you with your problem:
It depends on 3 factors: your connection speed, the amount of seeders/leechers, and the upload speed of those people. The 1st factor is self-explanatory: if you have a limited connection type, you won't be able to get the full downloads speeds from Bittorent. Things like uploading/downloading from someplace else while running BT can affect your download. The 2nd fator is also a major one. If there's just 3 people downloading from a guy with 56k, you won't be getting much from it, but if there's 100 seeds, your speeds should hopefully be far better than 50kb/sec, for example. Lastly, the upload speed goes with the 2nd point, since people's upload speeds can vary when there's many leechers.
So while I'm not entirely sure how to increase the speed from a BT link, what you can do is either wait a few minutes for a download to speed up (at times, BT downloads take a while before they start to increase), or you can restart the BT download and hope that it connects to the appropriate seeds. Hope this all helps
