To configure log settings, go to System Settings > Advanced > Device Log Setting.
Device log setting window

Configure the following settings and then select Apply:
Registered Device Logs
Roll log file when size exceeds Enter the log file size.
Range: 10 to 500 MB Default: 200 MB
Roll log files at a regular time Select to roll logs daily or weekly. When selecting daily, select the hour and minute value in the drop-down lists. When selecting weekly, select the day, hour, and minute value in the drop-down lists.
Upload logs using a standard file transfer protocol Select to upload logs and configure the following settings.
Upload Server Type Select one of FTP, SFTP, or SCP.
Upload Server IP Enter the IP address of the upload server.
Username Select the username that will be used to connect to the upload server.
Password Select the password that will be used to connect to the upload server.
Remote Directory Select the remote directory on the upload server where the log will be uploaded.
Upload Log Files Select to upload log files when they are rolled according to settings selected under Roll Logs or daily at a specific hour.
Upload rolled files in gzipped format Select to gzip the logs before uploading. This will result in smaller logs, and faster upload times.
Delete files after uploading Select to remove device log files from the FortiManager system after they have been uploaded to the Upload Server.
Local Device Log
Send the local event logs to FortiAnalyzer / FortiManager Select to send local event logs to another FortiAnalyzer or FortiManager device.
Server IP Enter the IP address of the FortiAnalyzer or FortiManager.
Upload Option Select to upload logs realtime or at a scheduled time. When selecting a scheduled time, you can specify the hour and minute to upload logs
Severity Level Select the minimum log severity level from the drop-down list.
Secure connection for log transmission Select to use a secure connection for log transmission.
File management
FortiManager allows you to configure automatic deletion of device log files, quarantined files, reports, and content archive files after a set period of time.
To configure automatic deletion settings, go to System Settings > Advanced > File Management.