How can I increase internet speed

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http://askubuntu.com – I use Ubuntu 11.10, and I connect internet via a ethernet card. I have problem about very slow internet speeds. The manager at my work place tried to slow down the internet speed but when I use Windows with some download manager the internet speed is really good enough or when I test the speed of internet my results are good. How can I do? Could you help me please? (HowTos)