Good news everyone, the Fall Creators Update for Windows 10 is finally here. It brings with it a whole bunch of new features and improvements to various parts of the Windows 10 experience (including a big mixed reality push), though the download takes up a significant amount of disk space. Unfortunately, the Fall Creators Update does not do a great job of cleaning up after itself when it is finished installing, but if you take matters into your own hands, you can free up a several gigabytes of disk space—around 20GB to 30GB, or even more.
That is pretty significant, especially if you are rocking a modestly sized solid state drive as your primary storage, such as a 256GB SSD. Depending on your setup, clearing out tens of gigabytes of disk space can take you away from the being on the brink of full capacity, to giving you some breathing room (or additional space to install more games!).
This is not difficult to do, either—it essentially involves Microsoft's built-in Disk Cleanup utility, which will now give you the option of deleting the previous version of Windows that you just upgraded from. To get started, click on Start and type Disk Cleanup, then right-click and select Run as administrator. You can also get there by going to My Computer and right-click on your main drive (usually C:\) and click Properties > Disk Cleanup.
The Disk Cleanup utility is capable of performing several disk housekeeping chores, such as removing temporary Internet files, emptying out the Recycle Bin, and so forth. Before you get started, however, click on the Clean up system files button. Disk Cleanup will reconfigure itself and add an option for Previous Windows Installation(s). Make sure you the check box is ticked, along with anything else you want to remove from your system, then click on OK.
Another way to do this after installing the Fall Creators Update is to open Settings > Storage. Under the Storage sense heading, click Change how we free up space. A new screen will come up. Select Delete previous versions of Windows and then click Clean now.
Your mileage will vary on how much disk space is actually reclaimed here, depending on how much background clutter you have accumulated before running Disk Cleanup. Also, bear in mind that nuking your previous Windows install means you can no longer roll back Windows if you run into a problem with the Fall Creators Update. That should not be an issue, especially since Microsoft will patch any bugs that are discovered after rolling it out to the masses. Even so, you may want to run the Fall Creators Updates for a few days first just to make sure it is working correctly.