How to upgrade this theme without losing the data I have on the free version

Hello, I was using Clean Fotografie free and I wasn't able to continue using it since it kept asking for an upgrade, ok, I bought it, they send me the theme files, but I would like to know how to upgrade the theme, no just install the new pro version. Clean Fotografie Pro is a child theme of Clean Fotografie, if I activate Clean Fotografie Pro it doesn't take my custom things from Clean Fotografie Free, Header is all set by default again, the custom CSS is not loaded, etc. To be honest, I didn't need the pro version, I just need to remove the Upgrade now message since that doesn't let me do what I need. I hope anyone can help me.