My system preferences does not have system update on it

Back up your data, check your applications for compatibility, and depending on which Mac model you have, click on Mojave, Catalina, or Big Sur. It needs to be at least a 2012 one, or a 2010 desktop Mac Pro upgraded with a Metal-capable graphics card, to run a newer OS.

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To be specific, you are wanting to upgrade your operating system, not update it. Two completely different tings.