You may have found that Windows 10 has sucked up a lot more storage space than you anticipated. In actual fact, it’s your old version of Windows hogging the space.
Microsoft has set things up so that your old Windows version is still there in the background, waiting to be rolled back to should you take against its latest version. Which is pretty nice of it, when you think about it.
For most people, though, Windows 10 will be just peachy, and you can afford to delete the old Windows files to make some extra space.
To do so, open the Disk Cleanup app (try typing cleanup in the Start menu). Now select the drive Windows is installed on and select OK to start scanning.
Look out for the option to delete Previous Windows Installation(s) and select it if present. Otherwise, select Clean up system files, which should in turn present you with the aforementioned deletion option. Go through the approval process, and you should find your hard drive now has a few GB of extra space.