How to update the Canvas theme

2. Delete the theme on your server

If you have done any customizations to your theme files, these customizations will be lost if you use this method. If you have not done customizations to the theme, or you are running a child theme you can:

1. Go to Appearance > Themes
2. Activate TwentyEleven (or another theme)
3. Delete the old theme
4. Upload new version via Appearance > Themes > Install Themes > Upload
5. Activate the new version

This is one of the methods described in the official Woo documentation on how to update a theme.

This should probably be done during off hours (late at night) so that it does not affect a website's functionality.  The website would display a generic theme until the steps are finished.