To check for an update to the Volumio software, open the web interface and drop down the gear menu at the top right. Select the System entry.
On the System page, click on the Check Updates button. If an update is available, you will see the details of the update, like this:
Click on Update Now. You will see a progress bar:
When the update completes, Volumio will automatically restart. After the webpage returns, it is important to refresh the webpage in your browser. This ensures that any updates to the user interface itself are updated in your browser.