Below is a detailed, safe walkthrough to get you from 10.13.6 to 10.15. Before doing anything, confirm your Mac can run Catalina.

If you’re still running macOS High Sierra 10.13.6 , you’ve likely enjoyed a stable, reliable system for years. However, as software evolves, you may find that newer apps, browser updates, and security patches are no longer supporting your current OS. Updating to macOS Catalina (10.15) is a logical jump—but it’s also a significant one.

Good luck, and enjoy your upgraded Mac experience!