DO NOT uninstall your PitchingCounter app until you export your data from it and import that data into the Pro app!!
IF you see a dialog asking for permission to read/write files you'll need to agree. You've already done this for writing data to the app directory when you installed the apps. But this is asking for permission to import/export the data to a different location. Due to how Android tries to keep apps from messing with other apps, I needed to write/read the data to a secondary location. When you give the app permission, you might need to back up one level, and then retry. It should work the second time.
To export your current data from Pitching Counter:
To import these files into PitchingCounterPro:
After you've imported the files, go look at the data in the Pro app and make sure you're happy with the look, and check the data to make sure you imported everything.
Once you've done this, THEN you can uninstall the free version of the app. I would recommend doing this, so that you don't accidentally update data in the free app. Merging the data is a bit of a pain. So to avoid that, just remove the free app once you're happy with the pro version...