HTC has released their first official Windows Mobile 6.5 Upgrade, which targets the Touch Pro2, initially a Windows Mobile 6.1 device.
The update is a Windows 'RUU' exe that will clear all data on your device and replace the current Operating System with the new one. Not much info on that, except for the fact that is is ROM version 1.86.401.0.
Download from the official HTC website, run the application and follow the instructions carefully! Make sure to backup contacts, emails, messages, call history.