The 8.1 update to Windows RT will be delivered via the Windows Store, however it is likely that a OS patch will first be required in order to allow the OS to be updated in this way - so, you'd first get an OS update delivered via Windows Update in the usual manner, this would then 'unlock' the 8.1 RT update in the Windows Store for installation. These updates are not year released, but are available only in preview form. You can get the preview for your Surface RT device via the Microsoft website, however please note it is a preview at the moment, so only install it if you are happy running a preview release Operating System.
You can probably hack your Surface RT to run a different OS yes (you can already jailbreak Windows RT on the surface), but you probably want to make sure you have a suitable 'touch enabled' OS so you can work with it appropriately, and make sure you have a 'way back'.