If you hold the Shift key and click the Options → Install Add-ons menu item, you'll automatically upgrade user-installed add-ons (of course, if any and if needed to).

However, doing this should not be required as user-installed add-ons are automatically upgraded too the first time you'll start XXE after upgrading the application.

The user is simply asked to confirm that she/he accepts to proceed with this automatic task.

If the user clicks Later, XXE will keep “nagging her/him” each time the application is started until all obsolete add-ons are upgraded or uninstalled (either automatically or “by hand”, using the "Install Add-ons" dialog box). An expert user who really wants to keep obsolete add-ons installed on her/his computer may choose to select "Don't ask me again".