If you purchase a Particle Designer 2.0 Upgrade license, you also need to have a Particle Designer 1.x license as well. If Particle Designer 1.x is installed on your machine then Particle Designer 2.0 should automatically find the license and register Particle Designer 2.0 successfully. If Particle Designer 1.x is not installed then you will be asked if you want to select the license file manually.
Selecting yes will allow you to navigate to the Particle Designer 1.x license file and select it. This will again then register the app.
If you don't have your Particle Designer 1.x license file anymore you can request it from our web page using the "Recover License" section.
You will need to provide the email address used when you purchased your Particle Designer 1.x license. You can recover all your licenses using this method.