Unfortunately, it is not currently possible to activate from the trial version of Riffstation. You will need to download the full version of Riffstation-desktop from the following relevant link:
Then use your activation details to activate Riffstation. You can retrieve your activation details using this link if needed. Make sure to use the email address linked with your purchase. If you purchased via Paypal, the email address linked with your Paypal account will be the same as the one linked with your purchase.