Note : Its always recommended to backup your Website, Theme, Database before updating. You can use this updraftplus plugin to have regular backups of your Website.
Updating the theme is very easy.
If you have setup the oAuth during the first Setup Wizard run, you will see all updated versions available to update in Dashboard -> Updates.
If you did not setup oAuth during first install, you can Click Envato Market link on bottom of left admin panel menu and follow on screen instructions. (Make sure you have Envato Market Plugin active, its in required plugins list, so 99% you already have it active.).
After updating the theme, just go to Appearance->plugins to update all plugins to their latest versions.
You can also visit this page for Updated theme update instructions.