how do i update a 2011 mac

D.I. Johnson has you covered.

But possible help if you're stuck...

Mostly you just need a more modern Browser than Safari on High Sierra like Firefox or Brave.

https://brave.com/

https://www.mozilla.org/en-US/firefox/83.0/system-requirements/

Firefox 83.0 System Requirements (mozilla.org)

Thanks to dialabrain…

FWIW, Firefox 109.0 (current version) runs in High Sierra.

https://www.mozilla.org/en-US/firefox/new/

Look into the Free LibreOffice, it handles MS Office files like Word & Excel, & Page Layout…

https://www.libreoffice.org/

A 2011 Mac cannot be upgraded to an OS newer than 10.13.6 High Sierra.