This is the easiest and fastest method to update theme. Do follow these steps to update by Envato Toolkit.

Step 1. Download Envato WordPress Toolkit here.

Step 2. Install and active the plugin in Dashboard >> Plugins >> Add new.

Step 3. Get your API keys.

Step 4. Dashboard >> Envato Toolkit >> input API keys (Marketplace Username &  Secret API Key).

Step 5. After input API keys, there will be “Themes” tab. Now you can update theme automatically.