how do I upgrade my OS from High Sierra 10.13.4?

Back up your data,, update to 10.13.6 in the Mac App Store, check your applications for compatibility, click here, and depending on which Mac model you have, then on the download link for Mojave, Catalina, Big Sur, or Monterey; it needs to be at least a 2012 one, or a 2010 desktop Mac Pro upgraded with a Metal-capable graphics card, to run any of them. If you get a Mac App Store preview page, change the https at the beginning of its address to macappstore.

Catalina and newer won't run 32-bit software; download and use Go64 as well as using the first link above.

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