After you install the paid version, you will notice there are now 2 different apps on your phone. To transfer all your lists and settings from the free version to the PRO version, you can use the Import / Export tool:
1. In the free app, go to Settings — Backup and tap Export.
2. Then open your PRO app and go to Settings — Backup and tap Import.
After you check the transfer really worked, you can delete the free version.
If you encounter any problems, please contact us at firstname.lastname@example.org.