Approximately 15GB to 18.5GB of available disk space for the installation. 2. Critical Pre-Upgrade Steps
On High Sierra 10.13.6, you will often not see the Catalina update in the standard "Software Update" window. You must typically find it in the . Upgrade to macOS Catalina. - Apple how to update macos high sierra 10.13.6 to 10.15
Apple provides a direct link to the Catalina installer, but it can be tricky to find via search. Approximately 15GB to 18
Never perform a major OS upgrade without a backup. If the installation fails, you could lose your files. Updating and Upgrading macOS High sierra - Apple Community how to update macos high sierra 10.13.6 to 10.15