How do I update my phone, when it won't take it through system update in my menu?

My note 5 wull not update. It hasnt had an update since 2016. How am i able to do so? Says system is up to date. And i know it isnt. Its working on android 6.1.0 or something like that. And it runs clear to let u know it needs updated badly. Am i able to do this on my own somehow...

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