High Sierra 10.13 update

If you're referring to updates, 10.13.6.

If you're referring to upgrades, it depends on what Mac model you have; the next-higher version requires at least a 2012 one, or a 2010 desktop Mac Pro upgraded with a Metal-capable graphics card.

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To tell you that, we need to know what year and model Mac you have.

Find that info by clicking the  (Apple) menu at the top-left of your screen and then select About This Mac.