Can I upgrade high Sierra 10.13.6 to Mojave 10.14

It depends on whether your Mac is compatible with macOS Mojave or not.

Try to install it by using this link (which will direct you to the Mac App Store): Download macOS Mojave from the App Store. It should notify you whether your Mac is supported or not.

Yes, if your computer is a 2012 or newer model, or a 2010 desktop Mac Pro upgraded with a Metal-capable graphics card.

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