Windows10Upgrade folder is created by the Upgrade Assistant when you downloaded the next Windows 10 Update manually instead of waiting for it to come from Microsoft Update website. Disk Cleanup doesn’t delete this folder despite it can be a few gigabytes in size: 
Here is how to remove the folder safely.
How to remove Windows10Upgrade folder in Windows 10
Follow the steps to remove the “weird” directory and free up some disk space:
- Go to Programs and Features.
- Find Windows 10 Upgrade Assistant published by Microsoft Corporation.
- Select it.
- Click Uninstall in Programs and Features window.
- Click Uninstall in Windows 10 Upgrade Assistant window.
After that Windows10Upgrade folder will be automatically removed.
If you don’t find the uninstaller in Programs and features, you can safely delete the folders from all drives manually:
Did this tutorial help you? If something is unclear or you have something to add, feel free to drop a comment! Thank you and have a nice day!