If you only want to delete or edit files, you have an easier alternative, connect to your server using WinSCP.
It works like an FTP, you can send/receive files, delete or edit them. All in explorer-like windows.
Anyways, from console you can do:
cd /var/log (--> To change directory)
dir (--> To view files)
dir *.gz (--> This shows you only the old logs. If you delete these files you'll only see )
rm -Rf /var/log/*.gz (--> Remove all past logs.
Be warned, using incorrectly rm -Rf can result in loss of data and havok!!!! )
But the above is not a long term solution.
The firewall config page:
https://your-efw:10443/cgi-bin/logs_config.cgi Should let you choose the days stored on logs.
Another option is to change the logrotate config.
nano /etc/logrotate.conf (--> To edit the logrotate options)
The third line says: "rotate 366"
These are the days stored on logs. If you only want 1 week of stored logs, you can change it to "rotate 7".
Once you are done, press Ctrl+O to save and Ctrl+X to exit. Restart and that's all
All these things can also be done on WinSCP.