I installed Ubuntu 15.04 but with earlier versions this happened too. The problem is, with HTTP or normal downloads like watching youtube the speed is like 20kB/s and with bittorrent I can achieve the full 600kB/s of my network, while in Windows 7 I can download the same files or watch the same videos and have them use the full speed of my network.

Any ideas? what do I have to change so HTTP works fast too? because I think the driver is not the problem since transmission works fine
Thanks

EDIT: And with ethernet cable everything works at full speed

seems like something is unstable with wifi. You can try alternative browser like switching from Firefox to Chromium-browser or change mini-pci adapter in laptop, most laptops have slot in back of laptop.

4 ways to get Wi-fi working on Linux