By default, Homey updates automatically. Homey downloads updates when they become available, and installs them in a reboot, at a time that you usually do not use your Homey (like at night).
Within Homey's Settings → Updates screen, you can choose to not automatically download and install these updates. THIS IS STRONGLY DISCOURAGED by us, as you might up with a Homey that is less safe or compatible. Only uncheck automatic updates when you know what you are doing, and understand the risks.
Within Settings → Updates you can also select to receive experimental updates. These might be less stable and tested than normal updates. Only check this box if you understand and accept that this may affect your Homey experience.