My bank says I have to up date my browser how do I do that

Which exact Mac do you have. Apple logo at top left>About this Mac…

If you cannot Upgrade further than you're at...

Mostly you just need a more modern Browser than Safari on Mojave, or 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)

Opera…

https://www.opera.com/download/requirements

Opera system requirements | Opera

Thanks to dialabrain…

Firefox 112 is now the current version. runs in High Sierra.

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