Below is the information about the 'Log rotation and aging'
Log rotation and aging prevent the Agent from filling up the host's file system.
Each Agent limits its number of logs to 5, rotating the log file index. Because Index 0 contains environment and start up information, it is never overwritten. Each of these 5 files is limited to whatever logfilesize is configured as <option> passed to the JVM as described above.
Because log file sizes and their number grow over time, the Agent purges logs files when:
A log file is older than 14 days
The combined size of all log files exceeds 1 GB of storage space
There are more than 1,000 log files
To prevent unnecessary delays in your application's start up, the Agent's bulk purge limit is set to delete a maximum of 50 of the oldest files. This logic is shared between bootstrap and core Agents, so in total 100 of the oldest files may be deleted at one time.
Review the below link in case you really want to modify the size of agent logs after the above description.