Good day to you!
Just like you, after installing Windows 10 I have been unhappily surprised with the fact that there was no way to turn off automatic updates in this system. For Pro (Professional) version users there is a button “Delay update”, but it provides no guarantees and updates keep on downloading and installing, however there are fewer of them.
After carrying out a small research I’ve chosen three working methods of disabling Windows 10 updates, which I will share with you further.
Disabling Windows 10 Update:
This is the easiest and universally applicable method that works on any of Windows 10 versions.
1. On the desktop, press “Windows” and “R” buttons simultaneously, “Windows” key looks something like this:

2. “Run” dialog window will appear, type “services.msc” into it and press “ОК”:

3. Find “Windows Update” on Windows Services list, usually it is located at the very end of it:

Choose this line (double click the left mouse button).
4. In “Properties” window you need to set “Disabled” for “Startup type”, press “Apply” button, click “Stop” button and then “OK” as the picture shows:

That’s it, Windows 10 Update is disabled and updates will no more be downloaded and installed automatically. If you want to turn automatic updates on, repeat the above mentioned actions, but choose “Startup type” = “Automatically” and then click “Start”.
Stopping Windows 10 updates, using Wi-Fi settings:
It sounds a bit odd, however, this is an ideal method for those who connect to the Internet, using Wi-Fi network. Windows 10 enables to set Wi-Fi network as limited (metered) connection, then the system won’t download updates, using such a network. Only Microsoft experts know, why there are no similar settings for a common wire connection, there can be no logical explanation of it. Well, let’s get down:
1. Press “Start” button, choose “Settings” line. In settings, open “Network and Internet” section and move to “Wi-Fi” tab:

We need “Advanced options” subsection, it is located below the list of available Wi-Fi networks, as shown on the picture above.
2. The second line will be “Metered connection”, turn it on:

That’s all, from now on Windows 10 will download and install no updates as long as you are connected to this Wi-Fi network. If you change a Wi-Fi network, you will need to repeat the settings for a new network.
Disabling Windows 10 updates, using third-party programs:
I mention this method only to warn you against using it. Nowadays, you can find numerous programs on the Internet, promising to disable Windows 10 updates and additionally carry out plenty of useful actions. Be careful while downloading and using such programs, many of them contain viruses and other scumware. Why taking risk if there are other safe methods?
If you still have any questions left or need some details - please, ask a question!