The best way to keep your Garmin smartwatch running the latest software is to enable automatic updates. To turn them on, hold down the middle left-hand watch button to enter the "Settings" menu. Using the lower left hand button, scroll down to "System" then press the top right button to enter that menu selection.
From there, scroll to "Software Update" and hit the top right-hand button to enter. Inside you'll see an option to toggle "Auto Update" on and off. Press the top right-hand button to turn it on. Below "Auto Update" you'll see an option to "Check for Updates", scroll down to highlight it, then hit the top right-hand button to perform a check. The software will then download and update if you're not running the latest version. However, you'll need to be connected to Wi-Fi to enable downloads – see below for more on that.