Follow these steps below to update theme via FTP:
Step 1. Login your Envato account. In Download tab, find Coaching WP and choose the Installable WordPress Theme (the WordPress file).
Step 2. Login your server and go to wp-content/themes folder to backup your Coaching WP theme folder if needed. The contents on your site will not be lost but if you have modified the code then the changes will be lost. You have to reapply them again after updating.
Step 3. Extract coaching.zip that you downloaded from themeforest.net
Step 4. Upload new theme folder coaching to wp-content/theme to override the existing files.