It's a pretty simple process, but there are a few best-practice steps to follow:
1) There is an upgrade path that's recommended to ensure that the databases update correctly. See the release-notes for the version you are interested in, and it will specify the versions you can upgrade from. If you are running an earlier release, you need to work your way backwards and look a the release-notes for that prior release, etc. We usually have a KB article that details this, but for some reason it's not showing up.
3) If you upgrade to 9.5 or higher you'll notice that you can't download the firmware directly, and must first read some special upgrade instructions. These have worked very well to prevent any issues.
As to which release, that depends to a certain degree on what your motivation for upgrading is. 9.4.3 is a rock-solid release and would be the next logical choice. 9.5.3 and 9.6.2 are also excellent. See the What's New articles posted for the releases to see what features were added.
9.7.0 is performing well, but if you use VOIP phones or warehouse scanners there are fixes in the other releases that make them better choices (I know..it's weird that a later version isn't a superset of everything earlier, but that's because we have multiple simultaneous releases)
It does take a scary long time for the upgrade (usually about 20minutes) so make sure an schedule an outage window. And we're here 24x7 if you need help with anything.
I was hoping to get some assistance with regards to this topic. I have tried updating our ZD1100 from 9.5 to 9.8 (could not find 9.6 on the support download page) twice and each time the device takes over an hour without any response with the status light flashing red throughout. After which I have to hard reboot the device which restores the previous version. Is there anything I am missing? I have followed the step by step directions on how to upgrade but with no success.
I require an upgrade to integrate our newly purchased t301s AP's so your assistance will be highly appreciated.