Full-Duplex allows devices to transmit and recieve at the same time while half-duplex is only one at a time; theoretically making full-duplex twice as fast.
The thing to keep in mind is that you can only use full-duplex in point-to-point communication such as router to router, router to PC, PC to switch, etc. If you're going through a hub then you have to use half-duplex because the media access is shared.
Also, you're going to be limited by the speed of the Internet connection anyway.