As you may notice you can't easily update from an AcyMailing Starter version to a paid version on WordPress. But don't worry this easy tutorial explains how to switch versions.
First of all you have to download the package of your plugin on our website, here is the documentation.
Secondly you have to uninstall AcyMailing Starter from your website, here are the steps:
Go to the menu Plugins -> Installed plugins
Search for AcyMailing then deactivate it.
Now that the plugin is deactivated click on delete. Your data isn't removed when the plugin is deleted.
Now that AcyMailing Starter is no longer on your website you can install the paid version you've previously downloaded from our website. Here is the documentation to install it.