OK so we have to uninstall first.
That's not what I've said:
It doesn't matter if you uninstall or not before
And I've said that, those installer that requires you to uninstall first, would clearly advise you to do it and will enforce this by not proceed if you don't uninstall first. LSGG was NOT included in my list of product where it's required to uninstall first, so you can safely assume LSGG doesn't require uninstalling first.
Do we also have to deactivate first?
First, installing/reinstalling doesn't have anything to do with the activation, which is never, ever lost "just" by Uninstalling. Deactivating a product is required (not really "required", best saying "suggested") only if you plan to reinstall on a DIFFERENT hardware.
But of course, exactly like in the case when if it was required uninstalling first, the installer would clearly alert to do so (so, again, not the case of LSGG), IF it was required to deactivate it first, the installer would clearly said so. Basically, the installers do know better: just trust them.
You are really making it way more complex than it is: to just upgrade a scenery, you don't need to do anything. Just run the installer.
If you WANT to uninstall, because it woud suit your sense of order, just do it. As I've said, it won't make any difference. And if it did, the installer would have been made in a way to make it very clear.