How do I clean up temporary files from my computer without deleting anything important?

If you're going to clean manually, be careful with the %temp% folder because some applications use it while they're running, and deleting files there can cause freezes or weird errors! The best thing is to use the system tool like they mentioned, but if you prefer to do it by hand, restart first and run the cleanup in safe mode so you can be sure nothing is using those files. You can also use programs like CCleaner that are more careful and show you what's going to be deleted before it does it, so you avoid unpleasant surprises.

I usually let Windows do the work in the background, but people sometimes get unnecessarily scared: the temporary files that the operating system generates can be deleted without any problem, most of them are designed to be disposable. What I do recommend is avoiding third-party tools like CCleaner that promise to work magic, because they're often more aggressive than necessary and can break things without you noticing. If you want to do it manually, open Run (Win+R), type `temp` and delete everything you can from that folder, but do it while you don't have heavy programs running. The system's native tool is the most sensible option though, because it's designed specifically for your version of Windows.