The audit log file has a maximum size of 100Mb. When the limit is reached, the file is wiped (or FIFO overwritten) and starts to fill up again. If rolling is enabled, then a backup of the file is taken before it is deleted. Up to nine rolled log files can be stored. e.g

• audit.log
• audit.log.1
• audit.log.2
• audit.log.3
• audit.log.4
• audit.log.5
• audit.log.6
• audit.log.7
• audit.log.8
• audit.log.9

Under Administration > Logs > SysLog, you can

• Export
• Download
• Print

Export can be a big file (e.g. I just tested it on a small lab NIOS box and it was 141Mb CSV file)

Download will give you a file called sysLog.tar.gz

Print will print a screen's worth of logs (about 8 pages).