In your address bar, type in 192.168.100.1. Hit Return of course. You will be in the modem configuration.

What kind of numbers are you getting? Click on Signal, what's your downstream and upstream levels?

Downstream should be 0v + or - 10v, and upstream not sure, I think 20 - 40 or something, but it's the down that affects downloads and the most important. If it's really low or high it's probably the lines outside.