Umm what service are you running?
If it's Cable/DSL: your provider has control over your speeds, but you can check your model to see what it's maxes are.
Dial-Up: Mixture of your modem and their modem
ISDN: You've got only a few possiblilities and you'd know if you had it.
T-1 up to 1.5mb up/down
T-3/5 don't remember
ATM don't remember either.