1° Step: You must to figure out your connection speed...
Ex.: For a connection of 512Kbps
Download speed: 512/8 = 64 kbps
Upload 512/16 = 32 -> 32×0.8 = 25,6 Kbps
2° Step: Changing the configurations of BitComet...
Go on options menu/ preferences/ connection and change:
1 - Global max download rate: 64 Kbps;
2 - Global max upload rate: 25 Kbps.
And done anything else just ask...