The easiest and safest way is to update through the Envato Toolkit plugin that comes packed with the theme.
In your WordPress admin dashboard you should see a section called Envato Toolkit. You need to connect your ThemeForest account to it and once you have done so, you’ll see here all available updates, always at one click away.
1. Navigate to the Envato Toolkit section in your WordPress admin.
2. To connect your ThemeForest account you'll need to enter the username in the "Maketplace Username" field and a input a Secret API Key.
3. The Secret API Key can be generate in your ThemeForest account, in the Settings > API Keys section:
4. Label it and click the "Generate API Key".
5. Copy the API Key and go back to your WordPress admin panel, to paste it.
6. Now that you've connected your ThemeForest account to your site, notice a 2nd tab called "Themes", you'll always be able to come here to update the theme.
7. Click the "update automatically" link and your theme will update to the latest version.