Theme support auto updates with use of Envato Market plugin that is bundled with theme. You can install this plugin like any other bundled plugin.
Next after installation & activation go to Envato Market menu in your admin area. There you will find instruction how to configure it.
If configuration went correctly you will now see all theme bought on ThemeForest, and you will have option to install & update them .
So you just need to update theme like you update your plugins. You can do it when you feel comfortable.