Microsoft Surface with Windows RT has builted in the Preview version of Office Home and Student 2013 RT. but the final full version of this suite is already available now. If you open charm bar and tap/click PC setting, there is no this update within metro version.
How to update Office 2013 preview to Full version on Windwos RT
* Go the Desktop and then go to Control Panel\System and Security\Windows Update, search for Windows Update, and choose “Install optional updates” in the search results.
* You will see “Update for microsoft office home & student 2013 RT preview (KB2748583))” which is about 586.00MB. Check on it and tap/click install button to apply. After making a reboot, you are able to access your updated Office Home & Student 2013 RT apps.