Some heads up, if your machine has downloaded the install files in the background, you can make an ISO before going ahead and for use on other machines. I intend making an image of my HDD's before upgrading to ease the pain should I need to revert back to W7 or W8.
Basically the W10 upgrade is saved in a hidden folder C:\$Windows.~BT/Sources.
(If you haven;t already you'll need to enable hidden folder view in explorer. Tools/Folder Options/View/Show hidden files, folders, drives)
Find the file Install.esd (should be around 2.5Gb)
Copy that file to a new folder and download ESD-Decrypter from the Microsoft site and unzip to the same folder where you put the Install.esd file.
Right click on the Decrypt command file and select Run as Administrator, you will then get a prompt for ISO creation.
Procedure detailed
here. and the Decrypt/ISO creation
here