How do i make my computer utilize the highest download speed that my connection will allow?

my download speed was 1.8 m/s, now it has slowly decreased a little to 1.6..etc .... is there something on my PC slowing down the speed that is being processed... i have a 15 MB connection through my provider.... could this be due to bent coax....??? or how can i get my downlaod speed back to normal.....