Navigate to the main window of the program.
There should be an "Upgrade" button at the bottom right corner.
If you click this button, a new window opens up with a big "Buy now" button on it.
Now you just need to click on the text below the button saying "Already purchased it? Unlock now" to reach the window where you can enter your serial number.
Afterwards, your simplitec Power Suite will be unlocked and you can use every feature of it immediately.
Simplitec team wishes you a lot of fun with the optimizations.