Based on your text, I’m assuming you changed the logo, pictures, layout, etc. through a “theme options” section in the WP Admin, instead of editing css/js/php files directly?
Whenever a theme is updated, typically (though this depends on theme) only the files are changed/overwritten. The types of changes you made are stored in the database and therefore shouldn’t be overwritten by a theme update.
I suggest making a child theme now and using child themes for every site you build going forward. Just an FYI though, when you create a child theme, you’ll have to set up the logo, colors, menus, etc. all over again if you set them up using theme options in the WP admin. At least this time though when you make any file-based changes they won’t be overwritten.