I think the argument has already been covered and the answer is negative but, perhaps with the current version, something has changed.
Now, leaving aside any novelty and ability to do this remotely and considering the duration of the operation and its complexity, I believe, however, that is not the case to do this remotely; if only because it increases the probability of failure and in case of failure anyway because you have to jump in the car :-)
You will need to be onsite as Arturo said because of the many possibilities. Also if you connect with SSL VPN will be disconencted and you most likely will need to recreate the SSL vpn certificate.
You may try to upgrade remote if are remotely controlling Local PC with CCA and software pack and which have secondary internet connection and console cable connected to the UC just in case.
You don't need to be onsite. Just take control of a local PC using VPN, remote desktop, or any similar Internet application, then do the update from there.
Paolo is correct. What I recommend is to use LogMeIn or RDP to get onto an on-site PC. Have your SWP zip on that PC. Launch CCA from that PC. As long as your routes are in place, shouldn't have an issue. I've assisted with dozens in this manner and never had an issue with a loss of data, since the actual upgrade is taking place locally, from a local machine.
Also Alexander is correct about modifying the SSL VPN, while using the SSL VPN. You similarly wouldn't want to make changes to your WAN interface when connected over it, would you?
And just as a footnote, and to reiterate, if you are running 8.2.0 in CCA 3.2, please please please update your CCA to 3.2.1 before upgrading to 8.6.0,
The document states: "CCA 3.2.1 is required for SWP8.6.0"
Sorry to "threadjack" but since we're on the topic of SWP upgrades and CCA, I really wanted to point this out, to save you from a support call for a number of issues.
I have done about a handful of upgrades over the VPN, and I must say it is a hair raising experience... So in saying that I wouldn't even advise of it, I only did it because I was lazy and got sick of driving everywhere and took that risk. But given how much can go wrong and go BADLY wrong you would be stark crazy to do it, which I just so happened to be at the time
I wouldn't even recommend doing it via remote desktop such as LogmeIN or Teamviewer or even RDP, a perfect example of that is, if the UC is routing the Internet and you loose connection to it and the connection does not restore after the upgrade, you can leave that system in an unusable state or partially completed, then you will have to go out there and deal with the problem after_the_fact... trust me not a good site in front of your client, it can make you look like a real tool (I'm not admitting to anything here what-so-ever either LOL)
Basically, major things such as an upgrade should be done locally, and leave the remote stuff for when you are giving someone locally assistance, that way you at least have remote eyes and hands to complete the task if something fails, NEVER leave something to chance, and this comes from experience