WordPress has a built-in feature to install themes and plugins by supplying a zip file. Unfortunately, you cannot upgrade a theme or plugin using the same process. Instead, WordPress will say « destination already exists » when trying to upgrade using a zip file and will fail to upgrade the theme or plugin.
Easy Theme and Plugin Upgrades fixes this limitation in WordPress by automatically upgrading the theme or plugin if it already exists.
While upgrading, a backup copy of the old theme or plugin is first created. This allows you to install the old version in case of problems with the new version.
Attention: Version 2.0.0 changed the functionality of the plugin. You are no longer required to select « Yes » from a drop down before the theme or plugin can be upgraded. The need for an upgrade is now detected automatically. So, if you are used to the old functionality of the plugin, do not be concerned about the absence of upgrade details on the theme and plugin upload pages. Simply upload the theme or plugin as if you were installing it, and the plugin will automatically handle upgrading as needed.
Page officielle : https://fr.wordpress.org/plugins/easy-theme-and-plugin-upgrades/