Here is the problems with Windows 10, it downloads update automatically and you have no say in it unlike the previous version of the Operating System. And the worst part is that most of the households subscribes to a monthly internet plan with data limit and many of them aren't even aware how their monthly allocation of data just disappeared. Here is how to have some control over the Windows 10 update
Preventing Automatic Downloading of the Update
To prevent Windows 10 from automatically downloading updates, you must set the internet connection as 'metered'. Windows 10 won't automatically download updates on any connection that have been set so. However, Windows will automatically download updates when the device gets connected to an 'unmetered' network.
To set a connection as 'metered', go to settings app and select 'Network & Internet'. Scroll down the list of Wifi networks available to find the 'Advanced Options' . In 'Advanced Options' turn on the 'Set as metered connection' option.
Choose How updates are delivered
In order to avoid load on Microsoft's network while proving updates and upgrades, they added a nifty mechanism into the Windows 10 which downloads "updates from and send updates to PCs local network and PCs on internet". This means that even after downloading and installing the updates, your PC then will send or upload parts of the update to other PCs on internet making you lose additional broadband data.
To turn this off, go to Settings app and to 'Update & Security' category in it. Choose 'Advanced Options' from the 'Windows Update' pane and scroll down to 'Choose how updates are delivered' and turn off receiving and sending updates 'from more than one place'.
Prevent Windows from rebooting automatically
You can now schedule Windows to reboot your computer after an update in Windows 10. This is very convenient considering that the previous versions wanted to reboot as soon as possible. You can make Windows to reboot on a schedule you choose by going to the Windows Update's 'Advanced Options' mentioned above and selecting 'Notify to schedule restart' instead of 'Automatic (recommended)
source: Life Hacker