Updating the theme can be done in 2 different ways. Both will lead to the same result, but only one is easier for some inexperienced clients.
Method 1: Using the official Envato Market Plugin. See tutorial.
Method 2: Download the theme from your ThemeForest Downloads section.
This method takes a bit longer and requires FTP or cPanel. First of all back to the theme. After making the backup you have to delete the theme from the server, upload the new theme archive, and unzip it under the /themes/ directory. That’s all.