For anyone contemplating upgrading their operating system (to Win10 or any upgrade) I would strongly recommend making a
disk image of your existing system first. Then if the upgrade doesn't work, or you don't like it, you can just install that disk image to immediately get back to where you were.
The process varies a bit depending on the disc imaging software you use, how your data and programs are organised on your hard disk or disks, and where you will store the image to, so you will need to do a bit of planning beforehand. Best to do a bit of swotting up disk images via Google to understand a bit more about it.
Lots of free software available to do disk imaging, your existing backup software may already do it. If not, a very popular and quite easy to use one is Macrium Reflect:
http://www.macrium.com/reflectfree.aspx (no connection with them, only that I use the product).
On my PC, in addition to daily backups of my data to a number of different destinations, every month (or if there are major updates from MS) I make a new disk image and save it to a USB drive which is then kept disconnected in a drawer. It only takes about 8 minutes for all Windows and Program files, all my data is on a separate hard disk.
I'm still on Win7 and have no intention of moving to Win10 for the forseeable future, too many problems being experienced by people plus security issues. When the end of the free upgrade period approaches, I plan on taking a disk image of my Win7 system, doing the Win10 upgrade (just to get my system registered with MS), save an image of that, then revert back to the Win7 image. The Win 10 image I can then keep until I decide to upgrade (or not).
David Miller - researching Miller, Hare, Walker, Bright (mostly Herts, Beds, Dorset and London)