Whether you're upgrading to the Windows 10 Insider Preview or the official build of the operating system, you'll notice a significant hit on hard drive space—up to 20 GB taken away from you. For those with older or even solid-state hard drives (SSDs), this can be a substantial hit.
Luckily, there's a super easy way to reclaim some, or possibly all, of this space back, and it's done with Windows' built-in Disk Cleanup utility.
To free up hard drive space, search for Disk Utility (or access it through the "Windows Administrative Tools" folder in the Start menu). From there, hit the option for "Clean up system files" and let Disk Cleanup relaunch.
Now you'll see options in the "Files to delete" list for "Previous Windows installation(s)" and "Temporary Windows installation files."
On my Windows 10 system, these two entries equaled 17 GB of space! Combine that with my very cluttered Recycle Bin, and I've now recovered over 21 GB of precious storage.
Just note that by clearing these two entries, you will no longer be able to roll back to your previous version of Windows. So make sure it's something you want to do before actually doing it.
Obviously, your mileage will vary with the amount of space you can clear, but in the end, you'll have more room for games, apps, videos, pictures... whatever have you.