How To: Activate Trillian Pro
Trillian has a single installer, which means that there aren't different installations for Trillian Pro versus Trillian Free - it's one file that you use to download and install. Your subscription status is recognized when you sign onto our network, assuming your information is entered correctly in your installed copy of Trillian.
Go to Preferences->Accounts and make sure you've entered your username, registered email address, and password. Once you've done this, it will indicate that you're a Pro subscriber.