Microsoft really doesn’t do itself much service in naming its products with Microsoft Office Home & Student 2013 RT Preview being quite a mouthful. However, you can update this preview version to the full version on your Microsoft Surface and knock off the last word in the title.
Fortunately, it’s not hard to undertake but helps if you know how so I made a short video:
Essentially, you need to get into the desktop instance of Windows Update, select the optional update for Microsoft Office 2013 and kick off the installation.
Bear in mind, this optional update is rather hefty at nearly 500MB so it might be a good idea to kick it off when you don’t need to be using your Windows RT tablet and have it connected to the charger as well.