After a successful upgrade of windows 10 to the latest edition  (currently 1803) it is easy to free up space on your Windows 10 ClassBook.

In the search bar type disk cleanup.

Click the button that says Clean up system files

Un-tick everything, then tick previous installation of windows as below.

Click delete files

Click yes

After the process is complete open file explorer and click This PC

You will see that you have somewhere around 11-13 GB of free space.