Back up your data, check your applications for compatibility, click here, and then on the download link for El Capitan. If you're trying to update to 10.10.5, check the Mac App Store's Updates tab.
Back up your data, check your applications for compatibility, click here, and then on the download link for El Capitan. If you're trying to update to 10.10.5, check the Mac App Store's Updates tab.