OPTA - Know the size of free on the internal partition

Hello,
How to know the free size on an internal partition of an arduino opta.
How to also know the size of a file.
I have not seen anything to do this in the Arduino_UnifiedStorage library
The goal, to make a datalogger in the internal memory, when the memory is full, delete the oldest files.
Sincerely
Matériel : Arduino OPTA