How do i set my thomson gateway to auto negotiation?

I got a router from plusnet on friday, thomson gateway. At first I could stream videos perfectly on my wirelessly connected laptop, I watched a programme on 4od without it stopping for buffering. But on Saturday, Sunday and this morning I have been unable to stream anything, it took me all day to watch a film (1hr 48mins) due to really slow buffering. I checked Ispeedometer at various times and I was only getting 100kbps, and when I checked out my PC connected by Ethernet cable it was getting the same. I heard I could set my router to auto negotiate for faster connection speeds, since some routers only give out 1Mbps to each device or something. I cant find this option in my Thomson Gateway's address where you have all the options. Please help (in not too technical language if possible).