The theme can be updated in any one of the following methods.
Automatic Update
You can use the Envato Market plugin to update the theme automatically. Instructions here: https://ibndawood.com/how-to-update-a-themeforest-wordpress-theme-or-a-codecanyon-wordpress-plugin/
Semi-automatic update
Sometimes automatic update might not work. You should install this plugin: Easy Theme and Plugin Upgrades , download the latest installable WP theme zip file from your Themeforest downloads page and then upload it via Appearance > Themes > Add New > Upload Theme and upload the zip file. The “easy upgrades” plugin will backup the old theme and install the new one.
Manual Update
You should download the latest installable WP theme from your ThemeForest downloads page, rename your current theme folder in wp-content/themes folder, unzip the downloaded WP theme from your Themeforest downloads page and upload it to wp-content/themes folder.
Please note that updating a theme will override any custom changes that you make to the parent theme. Hence we recommend using a child theme. A child theme is not meant to be updated and should contain only your custom changes.