Thanks for your response!
Sadly, I can’t delete the whole folder via FTP. That’s where I get the error messages. So, I can’t delete through wordpress, and I can’t delete server-side.
I have found it’s not just blocks.css it’s also
colors-dark.css
editor-blocks.css
editor-style.css
ie8.css
ie9.css
coffee.jpg
espresso.jpg
header.jpg
sandwich.jpg
svg-icons.svg
and the list keeps going and going.
I did try to upload different .css files like you suggested, but I get an error message that my permission is denied. So I can’t override the existing files either.
Any other ideas? Thanks again for helping me brainstorm!