update ios for macbook

Depending on how old your MacBook [or /Air, /Pro, etc] is..

.. there should be an 'upgrade installer' available from here:

• How to get old versions of macOS - Apple Support

https://support.apple.com/en-us/HT211683

These are downloads, and they come from an Apple server.

Best to use 'wired' internet, not wi-fi, due to size & time req'd.

However if your internet access gives no option, try the wi-fi.

Also use Safari browser, an older Mac system's browser should

be OK. Otherwise, using non-Apple web browser will not work

(or rarely) to download a working full installer. These take time.