All the new Garmin GPS's create .FIT files as well as .gpx files. .FIT files are used by the Garmin Connect app. They can't be deleted by the usual method of deletion in Basecamp.
In order to delete the files from your GPS, please follow the instructions below.
1. Connect your GPS to your Windows PC/Macbook
2. Once connected, go to Windows 'File Explorer' or Mac 'Finder' and 'explore' the Internal storage of the GPS by single/double clicking on the name of the GPS
3. Double click the 'Garmin folder'
4. Double click the 'Activities folder'
5. Delete the .FIT files
WE URGE GREAT CARE IN DOING THIS AND THIS IS DONE AT YOUR OWN RISK. WE DO NOT ACCEPT LIABILITY SHOULD YOU DELETE THE WRONG FOLDER OR FILE