Thanks for using Bitnami. We highly recommend you to create a server backup before doing any changes. You can get more information about it in the link below
The image you are using doesn't have the changes we included in the stack after helping this user. Can you ensure that you have the
expire_logs_days parameter in the MySQL's configuration?
Remember to restart the MySQL service after adding the
expire_logs_days parameter for changes to take effect
sudo /opt/bitnami/ctlscript.sh restart mysql
I think it is safer to let MySQL remove the non-required files than manually deleting them. In case the above do not help you to fix you issue, I recommend you to ask in the official MySQL forums as they can help you better with their product than we can.