In your WordPress dashboard, go to Appearance > Themes. At the top, click Add New, and then Upload Theme on the next page.
Click Choose File. Locate the vivienne-theme.zip file that came with your theme and upload it. (Note: your theme may have a version number behind it, such as vivienne-theme.3.0.4.zip. The child theme file will always be all lowercase.)
Click Install Now and wait for the theme to install. Activate the theme.
Alternate header option: If you would prefer your header to NOT display inside the navigation bar at the top of the page, don't install the theme file above.
Click here instead.