Download Visual Edit Pro
The link in your purchase email opens this page with your Visual Edit Pro key already in the field. You can also paste the key yourself. The plugin downloads after the licence server checks the key. The key is what opens the download, so this page works for as long as your licence is live, and again after it renews.
Install the plugin in WordPress
In WordPress: Plugins, Add New, Upload Plugin, choose visual-edit.zip, Install, Activate. If Visual Edit Lite is on the site, deactivate it afterwards: Pro already does everything Lite does.
Enter the key on the Plugins screen
On the Plugins screen, under Visual Edit Pro, paste the same key and activate it. A licence is registered to one domain, so before you use it on another site, deactivate it on the old one. A staging copy on its own domain counts as another site.
Updates arrive by themselves
While the licence is live, new versions arrive as ordinary WordPress plugin updates. When it lapses, the plugin keeps working with the Pro extras off, and no new versions arrive until it is renewed.