How to delete cache on Qnap

I have what I suspect is a corrupted cache as the scanner fails with disk full error even though there is 800Gb free. I know the Windows version of LMS quite well, but this is the first time I have used LMS directly on a QNAP (7.7.2) The precise error in the log is:
SQLite::db do failed: database or disk is full.
In windows there is a Control Panel, but how exactly do I achieve the same in this version. Thanks everyone.