If your OS is Windows, you can go the Start menu, and under Windows Administrative Tools, you can run Defragment and Optimize Drives and Disk Clean-up.
If that doesn't help, you can download some free software: CCleaner, BleachBit, and Wise Registry Cleaner. I've used these for years, no problems. CCleaner and Wise both clean the registry, but I run both because there are still things to clean up after I run one of them. Wise also has an optimize your computer thing, which is good to run.
With Bleachbit, don't check boxes next to passwords (browser and email), and don't check index or index files in your email client. There is no need for you to run, under System, free disk space. It doesn't free up space, it simply shreds deleted files. It takes awhile, so it's best to do that when you don't need the computer.
You can also run your Windows Defender and any anti-virus programs you may have. Malware Bytes is free, and also a good thing to download and run.