Check to see if you can ping to the outside like a domain from the Console tools, try to run the repair filesystem tool from the Extended tools in console (this will cause a reboot and w/ this ver. it works w/ NAS volumes). Also try to clear logs and any other older versions to free up space.
And then you can apply the update ISO file to your system, and that should let you update your system, and try to check if you have a firewall that block the connection between your system and the update server.