WordPress childtheme

A WordPress child theme is a theme that takes over functionality from another theme called the main theme. Child themes allow you to edit or add functionality to the main theme. A child theme is the safest and easiest way to modify an existing theme, whether you want to make small or very large changes. Instead of changing the theme files directly, you can create a child theme and use it to override the existing functionality.

How one creates a childtheme is explained at :
https://codex.wordpress.org/nl:Child_Thema's