For older Mac's, for example models from 2014, upgrading to the most recent version of macOS may not be a plausible option, as it often crashes the laptop and does not completely install. To prevent this from happening, refer to the following screenshots and notes relating to keeping your Mac updated.
A fully patched, but not upgraded Software Update window will look like this (to access this window simply click on Apple Menu > System Preferences > Software Update):
Ideally we want users that are having issues with updating to avoid clicking "Upgrade Now".
Because we still want want to update the Mac for other security updates or patches, clicking "More info..." under the "Other updates are available" section is still a preferred method of keeping your Mac up to date. This section is shown below: