Good luck, and enjoy your upgraded Mac experience!
One more tip: If your Mac has a mechanical hard drive (not SSD), Catalina will feel much slower than High Sierra. In that case, consider upgrading to an SSD or staying on Mojave. Double-check your specific model at everymac.com or Apple’s official support page. And remember – you can always download the Catalina installer from the App Store, even if Apple technically says your Mac is “vintage.” how to update macos high sierra 10.13.6 to 10.15
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. Good luck, and enjoy your upgraded Mac experience