I am on El Capitain 10.11.6 what version can I update my Mac too?

Compare your computer's specifications with those listed in the links under "Check compatibility" in the Related Article above; yours can run at least High Sierra.

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When I try to download High Sierra it says the install files are damaged...direct link from apple site.

Choose Applications from the Finder's Go menu, throw the existing installer away, restart the computer, and download it again.

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