Windows Cleanup Tips

 [1] The safest way is to let Windows do it

Go to Settings -> System -> Storage -> Temporary Files.

Select everything and click on Remove files. 

 [2] Use an external tool

 Example: PatchCleaner.

[3] Delete old files from the temporary directory

This directory is usually located in: C:\Users\<YOUR_USERNAME>\AppData\Local.

Here you can safely delete months or years old files. If they're still in use, Windows will prevent you from deleting them. 

If you're in doubt, skip what you were planning to do.