Right-click the file named 'PokerTracker' or 'PokerTracker.cfg' and select 'Open with.' and then choose 'Notepad' and click OK. Open PT4 and go 'File' -> 'Open User Data Directory' and a folder will open pointing to your PokerTracker 4 data directory.
If you were using a pre-commercial release version of PokerTracker 4 then PT4 is still registered using your PT4 pre-commercial release beta code and that code will need to be removed, via the instructions below, before you will be able to enter your purchased PT4 code: