Windows doesn't use the your bandwidth fully as it limits utilisation to 80 % for windows updates , spyware checks and all that other stuff.If you want to utilise the remaining 20 % follow the steps below.
- Open group policy editor [Start --> Run --> gpedit.msc ]
- Now go to administrative templates in the right pane.
- Now in the right side pane , click on network
- Go to QOS packet scheduler now
- There you will find the option " Limit reservable bandwidth "
- open it and check enable
- change the bandwidth limit from 20 % to 0%.