[Plextalk] deleting files and plextalk terms

I have just gotten this plextalk pocket. It is quite different from the booksense that my husband won. The thing that attracted me is that it is the first device that I was told you could actually edit on. But I notice that file structure and terminology seem to be different. One thing I notice is that in the delete settings, I go to delete a file, and it says I cannot delete this file. It is a file that I recorded on it with the internal microphone. What is the reason I cannot delete it? What am I doing wrong? Pam.