Install theme without losing the config of other themes

I recently installed a new theme (via upload). This activated the new theme, but at the same time, removed the old theme (or at least its configuration - I made some changes to some pages and changed script loading to local scripts).

Did I do something wrong or is there something I should note when installing new themes?

Changing themes shouldn’t overwrite any configuration that isn’t theme-specific. Custom settings should also be preserved from theme to theme.

Can you say more about the theme you switched from and to?

Sorry for getting back to you so late. I installed How to enable Taglist page · eddiesigner/liebling Wiki · GitHub coming from Alto. After installing the zip file, my Alto directory was empty.

How are you hosting your website? Might be worth seeing if they have a backup.