All of Ghost’s official themes can be updated to the latest version in Ghost Admin in just a few clicks, allowing you to access new features and theme improvements.
If you’re using an unmodified version of the default theme, Casper, your theme will be automatically updated. If you’re using an unmodified version of any other official theme, you can update to the latest version using this guide.
This method is not recommended if you have modified your theme, since it will overwrite your theme changes. Customized official themes should be updated manually, and you can find all theme repositories on GitHub.
From the Settings → Design page, click Change theme, and then click on the theme that you currently have installed:
Once you've selected your current theme, click Use → Install to install the latest theme version.