Before WordPress 5.5, if you wanted to update an existing plugin or theme that was not in the the WordPress repository (i.e. Premium Plugins and Themes), you had to go through the hassle of deleting the existing plugin or theme and then uploading the new zip file.
There was a nifty free plugin called Update Theme and Plugins from Zip File that helped with that, allowing you to easily upgrade plugins and themes from a zip file, bypassing the “destination already exists” error message. If you are using a version less than WordPress 5.5, you should definitely grab this plugin, as it will make your WordPress updating life a whole lot easier.
Now, introduced in WordPress 5.5, this functionality is built right in! You can use the Add New button for plugins and themes and upload new versions of existing plugins without requiring you to delete the old ones first. For those of you on WordPress 5.5+ and prefer to update your plugins and themes by manually uploading the zip files yourself, this is pretty sweet news and a real time saver.