: Double-click the installer app or boot from your USB drive (hold the Option key during startup).
If you're downloading from the Mac App Store, follow these steps:
Before downloading, ensure your Mac supports High Sierra. Generally, the following models are compatible: Late 2009 or newer MacBook Air/Pro: Late 2010 or newer iMac: Late 2009 or newer Mac mini: Mid 2010 or newer Mac Pro: Mid 2010 or newer 2. Official Download Methods
. It allows you to download older macOS firmwares and installers directly from Apple's catalog without compatibility restrictions. Manual Packages : Expert users can download individual packages like InstallAssistantAuto.pkg InstallESDDmg.pkg from Apple's servers and combine them using tools like Microsoft Community Hub
: Open the "Install macOS High Sierra" app from your Applications folder and follow the on-screen prompts to upgrade your current system.