All Windows 7, 8 and 8.1 eligible for Windows 10 update will automatically update to the new version of Window's if you got your computer is set to update automatically.
This is to get Window's users to try the new experience of Windows 10 and Windows wants to push users onto the new operating system and for anybody that receives updates automatically will soon switch on their computer and find Windows has been updated to the new version of Windows 10.
Even if you set it to manual in some devices Windows 10 will download and will prompt you before beginning if you'd like to upgrade to Windows 10 operating system in which you can refuse during set up.
This is to get Window's users to try the new experience of Windows 10 and Windows wants to push users onto the new operating system and for anybody that receives updates automatically will soon switch on their computer and find Windows has been updated to the new version of Windows 10.
Even if you set it to manual in some devices Windows 10 will download and will prompt you before beginning if you'd like to upgrade to Windows 10 operating system in which you can refuse during set up.
Don't panic Microsoft reassures you can revert back to your previous Windows 7,8,8.1 systems within 30 days of upgrading to Windows 10... Phew! Least you can still revert back to your old Windows system if you don't like it.