We've got until March, maybe April, when Microsoft will start pushing out the next version of Windows 10. As with last fall's upgrade, they'll probably be pretty aggressive, with the upgrade showing up on the majority of Windows devices in Windows Update as soon as it's released. *IF* Microsoft uses the upgrade process they're using with their Insider [Beta] builds [I think they probably will], if you don't have a lot of free disk space, now's the time to start watching the sales for a fast USB stick if you don't have one already. That's because the upgrade process looks like it uses 2 - 3 times the disk space your Windows system drive partition uses now -- it can & will use a USB stick for overflow if/as needed.
I wanted to give a heads-up, because I only saw a few good deals on faster USB sticks in all of 2017. A speedier USB stick isn't necessary of course, but my, does it make a difference. Note also that your Windows device may or may not be hurt here by the patches for Meltdown & Spectre -- this sort of I/O was severely impacted on one of my Windows tablets, but doesn't seem as terrible on anything else we have. Note also that while deals on fast SD & microSD cards are much more common that what I've seen for fast USB sticks, depending on your hardware, using one as overflow storage for a win10 upgrade may not work -- I've read reports that when the device restarted, it couldn't access the card & the upgrade process died.
You can reduce disk space used a bit by using an ISO of the new version of win10, putting the files on a USB stick or other internal or external drive. Because the new version was showing up immediately in Windows Update on our devices last time, I used the Insider's version ISO, which was available about a week before the general release, and about 2-3 weeks ahead of the general release ISO. [You could download the general release ISO using the Windows upgrade tool however.] The last Insider's version released before the general release of an upgrade has always been the same as the final build that will be used for that upgrade. Signing up for the Insider program is painless -- you basically just sign into the site using your Microsoft account, & check a few boxes -- your copy or copies of win10 won't start downloading Insider builds until you check the boxes in that copy of Windows 10, so there's no downside or risk really.
The way the upgrade worked with the latest Insider build this week was to 1st download roughly 5GB of data to the Windows\SoftwareDistribution\ folder. Note that this was using win10 Pro 32 bit, which is generally smaller than 64 bit versions. A copy of the files & folders as they'd appear on the system partition when the upgrade was finished was then created, including folders for installed software. At that point Windows was ready to be restarted -- setup completed by replacing the system partition layout with the new one, with all the old Windows files & folders now in C:\Windows.old, along with any files & folders that were not migrated to the new install.
This upgrade was performed on a win10 pro 32 bit VBox VM using a dynamically expanding VHD. That type of VHD is a single file that starts out very small, growing in size as disk space is needed. With the new Insider build installed, and all free space removed [the VHD was shrunken, or compacted is the proper term], the VHD is about 9 GB, roughly 1/2 GB smaller than it was with the older version Insider build. Note that the actual disk space used is a bit smaller than that, but because of non-movable files Windows intentionally installs away from the start of the partition [allegedly for better reliability], that's the smallest I can make that VHD.
Now the critical part is that before I shrunk [compacted] that VHD, it was about 30 GB -- that represents how much disk space the upgrade process needed & used, and it was notably larger than with prior version upgrades. Since all of the files & folders for installed software were included in that new copy, before the restart when/where the existing structure was replaced, I would expect that the disk space needed increases the more software you have installed, e.g. if you have 100GB of software, you'd likely need *at the least* another 100GB plus 10-15 GB for Windows 10.