Installing updates is supposed to be easy. Sure, it’s supposed to be – but that’s not always the case. This is especially true for the TMG firewall and also for UAG. Often there are little “gotcha’s” and workarounds that you’ll need to consider. Check out this article to get a leg up on the updating processes for these products
http://www.isaserver.org/articles-tutorials/installation-planning/best-practices-installing-updates-and-service-packs-forefront-uag-and-tmg.html
HTH,
Deb