How do I update my phone or computer, and why does restarting matter?

Reviewed answer

Turn on automatic updates, then restart when asked. Most fixes don't take effect until you do.

iPhone: Settings, General, Software Update. Turn on Automatic Updates.
Android: search Settings for "update". The menu name varies by maker. Also keep apps updating in the Play Store.
Mac: System Settings, General, Software Update. Windows: search Settings for "Windows Update".
Restart when asked, and about once a week anyway. Updates finish installing on restart, and a restart clears some attacks that live only in memory.
Update your browser too. If Chrome or Edge shows an update button, click it to relaunch.

Get help if

If a device says it can no longer update, or an "update" arrives by text, email, or website pop-up instead of through Settings, don't install it.