Trying to update my Photoshop CS6, but keep getting a failure with the code U44M1P7

If you had CS6 perpetual and have install  Creative cloud versions of Photoshop. Uninstall CS6 then install CS6 via the creative cloud desktop application.

If you only have perpetual CS6 I would suggest that you try installing CS6 on top of your current CS6. That should back level CS6 to version 13.0.  After you install CS6 use menu Help>Updates.  That  should update CS6 to version 13.0.1.3 Windows or 13.0.6 Mac and ACR to ACR 9.1.1 CS6 should be activated and your Plug-ins, Preferences presets and actions will still be installed.