One thing I really like about the Windows Surface RT is that it is set to automatically apply Windows Updates so the device is always be up to date. You can also check for updates anytime by swiping in from the right, selecting Settings and the Change PC Settings. Then from the Settings screen you can go to Windows Update.
The Windows Surface RT devices come installed with Office 2013 RT Preview and would be updated via the Windows Update process. A colleague just let me know that the update for Office 2013 RT is actually listed as an optional update and thus not applied automatically. If you want to apply the optional updates then you need to go to the Start page and search Settings for “Install optional updates”. This will run the desktop version of Windows Update and allow you to select and install the Office 2013 RT RTM version.