In this update I changed to using a .yml file to store user data so that server admins can view and edit values with ease.
Note that the yml file stored the UUID for the player and their stored xp, if you wish to convert this to a player username you will have to use a service such as https://namemc.com/
After reloading the plugin with the updated .jar file it should be safe to delete your "xps.dat" file in the plugin directory, however it would be a good idea to make sure all user data has been successfully transferred before deleting the old file