Here's the info from their FAQ:
"The e-smith subscription fee encompasses much more than our software. Rather than charging a set price for the software and then tacking on separate charges for technical support, upgrades and other items (some vendors even charge extra for a restore disc!), we keep it simple. We give you everything you need -- software, upgrades and unlimited technical support -- in one package. With e-smith, there are no hidden costs, no per-call or per-incident support fees and no per-user licenses."
That reads to me like the upgrades are included as part of their Subscription fee. You may be able to download a 'latest version' from the ftp sites when upgrades are published, but I don't know if non-supported versions of the software auto-upgrade during install.
There is a selection in one of the dialogs during the install that asks whether or not you are doing an upgrade. It reads to me as if it's asking to be sure you're not wanting to overwrite existing files.