Firstly, backing up your site content before making an update is always recommended.
Download the newest version on your download page at https://themeforest.net/downloads
We have four ways for updating Videotube theme:
1. Extract the videotube.zip file and override the videotube folder onto your hosting at wp-content/themes/ directory by FTP client tool.
2. OR log in to your backend, deactivate and delete the videotube old theme, and re-install the new file (videotube.zip) that you just downloaded.
3. OR using the Envato Market plugin, the plugin allows you to be able to update all items that you purchased from envato market (themeforest and codecanyon.net are supported), here is official discussion about this plugin https://forums.envato.com/t/envato-market-wordpress-plugin-beta/21639
4. OR using the built-in update feature.
Question: how about my modification if I update the theme?
- The update will override the newest version to your old version, so, if you modified the theme, these changes will be lost.
- The update won’t lost any settings you made in the Theme Options panel.
Question: How can I keep my modification?
I highly encourage you to activate the child theme which can be found in the purchase package, called “videotube-child.zip”, and you can modify the parent theme via child theme, once updated the theme to newest version, your changes won’t be lost.
Read more about WordPress child theme here https://codex.wordpress.org/Child_Themes