You have 3 options for updating your theme:
Dashboard Updates: While automatic updates aren’t included inside the theme by default (for important reasons) you can setup automatic updates via the Envato Market plugin which is a free plugin for updating your products purchased on ThemeForest. If you don’t have experience with the plugin please view the Envato Market Plugin Guide.
FTP: Alternatively you can always re-download the theme, extract and update the theme files via FTP.
Delete & Re-install: You can also just re-download the theme from ThemeForest, log into WordPress and temporarily switch to a default WordPress theme, delete the theme from your live site and then re-installl the theme.