There isn't a way to convert Features into Stories. You can convert a Story to a Feature. You can also convert a Feature to higher level portfolio item, but not a Feature to a Story.
One way to get this done would be to export your features using the Excel add-in, then convert the data in the excel and import it back as User Stories into the project you would like. I'm not sure if that's what you will want to, but technically this kind of features export, then user story import will essentially serve as a 'conversion'. If you do choose to do that this way, then you may want to decide which fields of the feature to export, you probably will also need to export a few stories just to get a template for your stories, then you will need to copy the data from the export feature sheet to the story template sheet, you'll need to make sure you are satisfying all the story field you need (plus required fields) and then import it.
I hope this helps.
Let us know.