You just need to go to the support.paloaltonetworks.com site and login. There you'll find all of the dynamic updates and software updates that you actually need for this. As for the content update, you'll simply download the the Apps + Threats bundle and install the latest version (8374-6538 at the moment). You should take the time to install the updates to the other dynamic updates that you have subscriptions for as well; if you're paying for those subscriptions and never updating them you're just throwing money in the garbage.
All of these updates can be done offline without issue, as you never really require an internet connection to do any of it. It certainly helps make the process quicker, but it's not a requirement.
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