Update: A colleague of mine pointed out that the idea that QOS takes up 20% of the bandwidth is actually a myth. Microsoft has a official answer to this which you can read here and it has also been denied by LifeHacker . Edit the setting at your own risk.
For its own use, Microsoft reserves 20% of your bandwidth by default for QOS or quality of service like Windows updates. Well, I usually don’t use Windows Update every day and don’t think most users use it, so why reserve bandwidth for it? To remove this limitation, open the Run interface and type gpedit.msc:
The Group Policy Editor window will open. Under Local Computer Policy, select Computer Configuration Administrative Templates Network QOS Package Scheduler Limit Reserved Bandwidth. My screenshot below should help you if you get lost in the navigation tree:
This will open the bandwidth reservation properties window and you will see that it is not configured by default.
… By default, the package scheduler limits the system to 20 percent of the connection bandwidth, but you can use this parameter to override the default.
I have not tested the results of this setting yet. In theory, this should add 20% to your bandwidth by removing this limitation.