First, let's try to see what's taking all that bandwidth. Here
's a link to a trial version of Track4Win. If you select the piechart view in it, you can at least see what program is eating the majority of your bandwidth. (I couldn't quickly find an app that would show usage amount by program)
There's a couple ways to conserve bandwitdh, most notably, disconnect from the internet
You can make a shortcut on your desktop to your network connections so that you can disable the connection. (I use this for my downstairs desktop when I'm not downstairs).
Do you have a firewall software that enables you to block all traffic? There's Comodo Firewall
which will do just that so that you don't have to disable and re-enable your adapter.
I would get Track4Win, see what's eating bandwith. If it's a program that you don't need to have running, task manager and close it. When you're away from your computer, disable the connection or set the firewall to stop all traffic.