I had NAS4Free server version x64_9.0.0.1.188 installed on a server and wanted to upgrade it to the latest version before moving into production.

I’m assuming you already have a ZFS (or other filesystem) share mounted on the server. And that SSH is enabled.

Copy the file to your share – I used WinSCP as it 1.) works and 2.) is free and 3.) I’m used to it.
SSH to the NAS and run the following:
/etc/rc.firmware enable
/etc/rc.firmware upgrade /path/to/img/file.img

The server will then reboot and you’ll be running the newest version.

ZFS tuning on freenas nas4free – I’ll split this out eventually.
http://forums.nas4free.org/viewtopic.php?f=55&t=26
# mkdir /mnt/data/zfskerntune
# cd /mnt/data/zfskerntune
# fetch http://www.kav91.com/nas4free/zfskerntune-20111022-nas4freeKav91.tar.gz
# tar xvf zfskerntune-20111022-nas4freeKav91.tar.gz
# cd zfskerntune
# ./zfskerntune-install.php