Can anyone suggest the proper settings for power management for such kind of problem.Just for a simple reason of downloading a lot of electricity is wasted if the PC is kept running for long hours.
You have to have your computer awake to download.
You can try a downloadmanager that can put your computer to sleep when the download is complete.
I would be very wary of torrent sites, apart from being linked with piracy the files on them can contain anything.