Hi!
I have been working on the old version of the theme "Epsilon 1.0.4" for a long time
In the theme files, I configure the "ssl" styles manually, the "head header item search" files were changed... "
I really want to switch to the new 1.1.9, but it's scary that when I update all my settings will disappear.
How do I update so that all my manual changes in files are not reset to zero?
Tell us step by step how to do it?

Create child theme and do modifications in child.
When you update theme, it will nit touch modified files and you optionally just need to update files you need

I found a topic on the website, "How to create a child theme."
Thank you for the hint

Np, good luck.
This may be even more helpful:

https://osclasspoint.com/blog/osclass-create-child-theme-b21