When you would ask are there companies claiming that there software will increase download speed with upt to 300% I would say yes, However only when.you believe in father Christmas is really alive, then you will also believe these software companies.
When you have a dial-up connection, you might have some benefit
Download speed depends also from what website you are downloading. When you for example download form
http://www.download.com you will get about 1/3 of your normal download speed. This is because it is a very poplular site and many are downloading from that site at the same time.
Your download speed depends mainly of hw fast your internet connection is.
I have an inernet connecdtion of 10MBps with a download speed of 1.2MBps. That speed I never get. between 600 and 1000kbps is normal. only at download com, I will be happy with 300kbps.
Do a speed test. This is the best there ishttp://www.speedtest.net/

u can use IDM.
many p2p softwares are there to download torrent files very easily