OFF: The highest possible rank and is intended to turn off logging.
ERROR: Designates error events that might still allow the application to continue running.
WARN: Designates potentially harmful situations.
INFO: Designates informational messages that highlight the progress of the application at coarse-grained level.
DEBUG: Designates fine-grained informational events that are most useful to debug an application.
TRACE: Designates finer-grained informational events than the DEBUG.
ALL: All levels including custom levels.
For more guidance on which level to use, see Coding Conventions#Logging
For modifying the log output of a running client, you may use a custom log4j config file by setting a system property at startup. Besu's logging doc provides good documentation on how to configure logging in Besu.