Updating your WordPress Theme to the latest version is highly recommended and is very simple. You’ll get latest features and you’ll also be up-to-date with any security patches.
Now, updating your theme in WordPress is made very simple for you. Just go to Dashboard > Updates and select your theme, then click the Update Themes button.
Example to update Marlin theme:
or You can also navigate from Appearance > Themes and click update now.
To take a manual update, please refer to this article.