Hi Linda,
Thanks so much for your interest in Events Calendar PRO! You shouldn’t ever experience any data loss or other setbacks from upgrading one of our plugins or moving from a free to a premium product. Your events and plugin settings are all stored safely in your WordPress database, and adding or removing plugins won’t disrupt this data. (In addition, Events Calendar PRO runs alongside the core plugin The Events Calendar to build upon its functionality, so you won’t even need to uninstall your existing plugins.) Feel free to purchase without fear–and know that we’re here over in the support forums should you have any questions or concerns along the way! 🙂
I hope that helps to set your mind at ease! Thanks again for stopping by, and don’t hesitate to follow up if there’s anything else we can assist with!