Applications Manager begins to purge log files after the $AW_HOME/log or %AW_HOME%\log directory reaches 500MB. This value can be increased beyond 500MB using an Awenv.ini parameter.
add the following variable to the $AW_HOME/site/awenv.ini or %AW_HOME%\site\awenv.ini file to increase the directory size.
In the [default] section of the Awenv.ini file, add the following line LogDirectoryPurgeSize=1024
This will increase the purge size to 1024MB, this number may be modified to fit your log file storage needs.