How to change subdirectory name?

I installed WP in its own subdirectory which I named “/blog”. Now I want to change the name of the subdirectory. I figured (incorrectly) that I just had to rename the directory and change the URI in General Options but in doing so, I’ve lost my WP theme and can’t log in anymore. I renamed the subdirectory back to “blog” but that didn’t work.

Does anyone know the best way to correct this problem?

It’s a recent install and wouldn’t kill me to reinstall but I’d rather not.

Thanks