To change the log level at runtime use:
# This is for the internal Akka actors and classic Akka logging
curl -X PUT <akkaManagementEndpoint>/loglevel/akka?level=DEBUG
# This is for the internal Akka actors and classic Akka logging
curl -X PUT <akkaManagementEndpoint>/loglevel/logback?logger=<loggerName>&level=DEBUG
where <loggerName> is the name of a specific logger that has to have been created in the code itself.
GETting the same endpoints w/o the level query parameters returns the actual logging level for that logger.