The above advice is good, but will really get you nowhere until you do this:
First thing, set up a static IP address for your computer and all the other devices that connect to your network. You need to do this because by default, your modem has your computer talk to the internet by assigning the computer a random IP address each time it or the modem starts up. Think of the IP address as a door. Being presented with random doors confuses bittorrent applications because they want to use the same door each time.
Next, you need to forward the port that your bittorrent application wants to use. The port is like the bittorrent application’s key to the IP door – ports allow programs through firewalls. You could forward the port without setting up a static IP address, and it would still help just as much with your dl speed, but then you’d have to forward the port each time you restarted your computer and each time your modem resets itself, because you’ve been given a new door and so need to arrange for a new key. So I recommend setting up the static IP address(es) first.
The bittorrent application will give you the port it wants you to use, or you can make one up. It’s four or five digits, and can usually be found somewhere under “Preferences”. Then plug that number in, along with your IP address, to your router’s firewall settings pane. You get to this by typing your computer’s IP address into the URL bar, and going to it as though it were a webpage. You might need a username and password from your internet service provider to access this; just call them and explain that you are trying to alter your firewall settings manually and they’ll know what you’re talking about. They can also guide you through the port forwarding process if you ask.
You will see your speeds increase quite a bit.