'ls' will list the files and folders in the folder of current focus.
'ls <path>' will list the contents of the folder at the end of the path
'rm -r <folder name>' will remove the target folder and everything in it recursively.
If the user you're logged in as doesn't have the privs, elevate the rights by using
'sudo rm -r <folder name>'
Don't wipe out the root folder /var/www/brewpi/data or wherever your logs are stored, just delete the individual run folders.
And look into
WinSCP.
It's the bomb for remote file management .
I use it exclusively across my RPi fleet, as I can open simultaneous sessions to multiple machines if I have something I want to distribute from my development system to the rest.
It's much easier to paw around your SD card than using CLI stuff...
Cheers!