Update-Button
after somebody purchases the Pro Version she/he will receive some kind of "license-key-file".
This License may be uploaded using the Pro-Interface and saved on the server
The next step would be some kind of "Update-Button"
You are sending every customer an email containing credentials for downloading?
implement a small script on that Update-Page that checks if there is an Update for the currently used Pro-Version
If there is an Update: Use the credentials from the Update page to download the update to the server and also to the admins workstation.
Invoke a checksum-check (md5 AND sha256) for installed files and if ALL installed files match you can start the update
If MD5 and/or sha256 checksums differ the admin has changed something:
Print a list of changed files and abort the "auto-update"
the admin knows he has to do a manual update and also has a list of files he has changed
also show the list of available system-updates on that interface:
we admins want to get reminded - there are security-updates for the system
This makes the update procedure easier for not so tech savvy users - some kind of "two-clicks-update"
AND: users if the small (GPL) version will see all of the Buttons of the "Pro" interface
But not "useable" as they first have to purchase the license -> so they get redirected to the "buy now" ->
they buy -> receive the license -> upload the license to the "small" -> and may invoke the upgrade-procedure to the Pro
<EDIT>
users of the annual license will also be able to check if there is an update
but as the "license" timed-out they won't be able to start it unless they renew as their credentials are invalid
<EDIT>
Greetings
Mike