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.
With this plugin you’re able update your WordPress theme or plugin very EASY, without the loss of data!
Plugin can be downloaded here: https://wordpress.org/plugins/easy-theme-and-plugin-upgrades/