how can I Update my OS X El Capitan 10.11.6, please?

Which MacBook do you have? See About This Mac in the Apple () menu.

This will determine how far you can upgrade the operating system. For instance,

• You cannot upgrade a MacBook Pro (13-inch, Mid 2009) past El Capitan.
• You can upgrade a MacBook Pro (Retina, 13-inch, Early 2015) to Monterey.

Back up your data, check the application compatibility table, click here, and then on the download link for High Sierra.

(248010)

If you upgrade to High Sierra, you may wish to install

Firefox 115 ESR. It isn't getting new features any more, but it still might help you with Web sites that don't work well with, or that complain about, the old version of Safari in High Sierra.

https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support

iTunes 12.8.3

https://www.apple.com/itunes/