Recommended Method

You don’t have to change anything in the database. Follow these steps:

1. Activate a default WordPress theme (e.g. twentyseventeen) – that is any theme other than the child theme you are going to rename.

2. Rename your child Themes folder name and child theme’s name in style.css file.

3. Now activate the child theme.

That’s all, WordPress will update related info. in the Database autometically.

Note: You’ve already figured out step-2 correctly. Just need to follow step-1 before step-2 and then step-3 afterwards. That’s all.

Database Method:

It’s also possible to change the theme name from the database after following step-2 above. Sometimes it’s helpful in case you’ve already changed the theme name & now can’t access the site because WordPress has a different theme name in the Database.

In this case, know that WordPress saves two values in the wp_options table. One is with the option_name = stylesheet and the other one is the option_name = template.

If it’s not a child theme, then both the values are same. For a child theme however, option_name = stylesheet will have option_value = your-current-child-theme-name and option_name = template will have option_value = parent-theme-name.

So if you change these two values accordingly, it’ll work as well. You can use PHPMyAdmin, or the following MySQL query:

update wp_options set option_value="new-child-theme-name" where option_name="stylesheet";

update wp_options set option_value="parent-theme-name" where option_name="template";

replace new-child-theme-name and parent-theme-name accordingly in the above query.