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There are 3 ways to Update the theme:
First of all, do a backup on your local computer. There is a lot of tool and plugins available to help you to do this. Just find one with a good rating and get it set up now, not later: https://wordpress.org/plugins/search.php?q=backup+wp
ALWAYS make a backup of your entire site before you update. Usually. the update installs within seconds and cause zero problems, but it's better to be safe than sorry.
How to upgrade?
The first thing to know is that if you have modified PHP, CSS, JS files into the core theme, the update will overwrite what you did (that's the reason we suggest doing your modifications in the child theme).