Delete caching files without backend access

Hi there,
I just tried to update my used theme (“hueman”) but forgot to disable caching in wp fastest cache before.
Now I cant access the backend (white screen of death) but the blog still shows up normally in frontend, even after renaming the theme folder and child theme folder via ftp.

How do I delete the caching files and/or deactivate wp fastest cache without access to backend for troubleshooting issues as it might be the course for the error?
Unfortunately I seem to not be able to find a how-to.