We mentioned a few days ago that Sprint would be pushing the May 7392 OS update on May 24th and sure enough, we just got the notification.
The update addresses fraudulent security certificates and doesn't seem to offer any new functionality, though we'll update if we find any on the HTC ROM side. To update, just plug your Arrive into your computer and sync and/or hop into Settings --> Phone --> Update and make it check for an update.
Say what you want, but at least with T-Mobile and Sprint here in the U.S., there's no drama.
Update: Looking at the "About" info before/after and we can confirm that only the OS is updated, there is no firmware revision, no new radio software nor new bootloader.
Thanks, @tiggscolo, for the heads up