You can easily update to the latest theme version, without downloading it from themeforest, and manually uploading it to your server using the 'Envato Market' plugin.
To update using the Envato market plugin:
Go to Envato market plugin and click 'generate a personal token' to add your token if you haven't already.
You will be transferred to Envato Market's site in order to generate your token.
On that page, you can leave the permissions at their defaults. Grab your token and paste it in the 'Token' text box and click 'Save Changes'.
After that you should see all your purchases from Envato in the plugin's page, and have the option to update in one click:
