[wlug] help with network connection please

I have installed Breezy badger on my other computer and was working well - I then moved the computer upstairs and now cannot connect to the network that I have. I had the same problem with windows and fixed this by changing the speed from 100BaseT full duplex to 10BaseT full duplex. I think that the problem is the poor quality of the network cable. How do I change the connection speed with Ubuntu? I am a newbie so will need simple instructions Thanks John