Before starting with child themes
We highly recommend to create a child theme if you want to customize any of our themes. By doing this, you will keep your custom work separate from the main theme, so when you are ready for an update there wont be any overwriting of the main theme files. So if the custom work stays in the child theme, you can update the whole parent theme, without even worrying about what files or what bit of files you have to update. Just copy in bulk and you are ready to go. We do advise you to backup everything before any update/upgrade, just in case. Better to be safe than sorry.
You can also find more information about creating a backup on wordpress official page.