Is it possible to upgrade my license to allow more riders?
Yes, go into Analyzer's Help section and click on the Upgrade PerfPRO link. You also click on the upgrade link within Studio in the Trainer Setup options. The cost of an upgrade is roughly the difference between the two license prices.
From there follow through the steps within Analyzer, which eventually deactivates the license on your machine so you may enter the new code after purchasing the upgrade. PerfPRO will also email you your current license code in case you change your mind. In that case you may re-activate using your existing code in that email and continue on.
After purchasing the upgrade, enter your new code in Analyzer and discard the old code as it is no longer valid.
Contact support if you run into any issues.